diff --git a/benchmark/chusql-engine/src/Main.hs b/benchmark/chusql-engine/src/Main.hs
index 7222914..44f1fa9 100644
--- a/benchmark/chusql-engine/src/Main.hs
+++ b/benchmark/chusql-engine/src/Main.hs
@@ -4,13 +4,16 @@ import ChuSQL.Algebra.Eval (evalRelOp)
 import ChuSQL.Algebra.Optimize (optimize)
 import ChuSQL.Algebra.Planner (translate)
 import ChuSQL.Model
-import ChuSQL.Syntax.Parser (parseQuery)
+import ChuSQL.Syntax.Parser (parseStatement)
 import Control.Exception (evaluate)
 import Data.IORef (IORef, newIORef, readIORef)
 import System.CPUTime (getCPUTime)
 import System.Environment (getArgs)
 import Text.Printf (printf)
 
+-- 性能基准：同一批语句，比较优化前后的耗时。
+
+-- | 造一张 users 表
 mkUsers :: Int -> Table
 mkUsers n =
     Table
@@ -22,6 +25,7 @@ mkUsers n =
             ]
         }
 
+-- | 造一张 orders 表
 mkOrders :: Int -> Int -> Table
 mkOrders n m =
     Table
@@ -33,37 +37,41 @@ mkOrders n m =
             ]
         }
 
+-- | 结果校验和（防被优化掉）
 checksum :: Either String [Row] -> Int
 checksum (Left _) = -1
 checksum (Right rows) = go 0 rows
   where
+    -- \| 累加行长
     go acc [] = acc
     go acc (r : rs) = go (acc + length r) rs
 
+-- | 结果行数
 rowCount :: Either String [Row] -> Int
 rowCount (Left _) = -1
 rowCount (Right rows) = length rows
 
--- salt 是从 IORef 里读出来的：有了这个"IO 里来的"依赖，GHC 就没法把整段纯计算
--- 提到循环外只算一次 —— 否则批量计时会把 1 次的开销除以 k，测出 0.000 ms 这种假数据
+-- | 跑一次，返回校验和
 runOnce :: IORef String -> Database -> String -> Bool -> IO Int
 runOnce saltRef db sql useOpt = do
     salt <- readIORef saltRef
-    let result = case parseQuery (sql ++ salt) >>= translate of
+    let result = case parseStatement (sql ++ salt) >>= translate of
             Left e -> Left e
             Right plan -> evalRelOp db (if useOpt then optimize db plan else plan)
     forced <- evaluate (checksum result)
     return forced
 
+-- | 跑一次，返回行数
 resultRows :: IORef String -> Database -> String -> Bool -> IO Int
 resultRows saltRef db sql useOpt = do
     salt <- readIORef saltRef
-    let result = case parseQuery (sql ++ salt) >>= translate of
+    let result = case parseStatement (sql ++ salt) >>= translate of
             Left e -> Left e
             Right plan -> evalRelOp db (if useOpt then optimize db plan else plan)
     _ <- evaluate (checksum result)
     return (rowCount result)
 
+-- | 量一段 IO 的 CPU 时间
 timed :: IO a -> IO Double
 timed act = do
     t0 <- getCPUTime
@@ -71,13 +79,16 @@ timed act = do
     t1 <- getCPUTime
     return (fromIntegral (t1 - t0) / 1e12)
 
+-- | 加倍批量次数再折算单次
 benchOp :: Double -> IO Int -> IO (Double, Int)
 benchOp target act = loop 1
   where
+    -- \| 批次翻倍直到超过目标
     loop k = do
         t <- timed (mapM_ (const act) [1 .. k])
         if t < target then loop (k * 2) else return (t / fromIntegral k, k)
 
+-- | 打印一个用例的对比
 report :: IORef String -> Database -> Double -> String -> IO ()
 report saltRef db target sql = do
     nUn <- resultRows saltRef db sql False
@@ -107,6 +118,7 @@ queries =
 warmupSql :: String
 warmupSql = "SELECT name FROM users"
 
+-- | 基准入口
 main :: IO ()
 main = do
     args <- getArgs
diff --git a/chusql-engine/app/Main.hs b/chusql-engine/app/Main.hs
index 0afccac..1928ef2 100644
--- a/chusql-engine/app/Main.hs
+++ b/chusql-engine/app/Main.hs
@@ -8,6 +8,8 @@ import ChuSQL.Model
 import ChuSQL.Syntax.AST
 import ChuSQL.Syntax.Parser
 
+-- 命令行演示：跑几条语句，打印结果与优化前后的计划。
+
 users :: Table
 users =
     Table
@@ -35,17 +37,18 @@ orders =
 db :: Database
 db = [("users", users), ("orders", orders)]
 
+-- | 演示入口
 main :: IO ()
 main = do
     putStrLn "==================== Engine ====================="
     let q1 = makeSelect ["name"] "users" (Just (Gt (Col "age") (LitInt 18)))
-    print (rowsOf (runQuery db q1))
+    print (rowsOf (runStatement db q1))
 
     let q2 = makeSelect ["*"] "users" Nothing
-    print (rowsOf (runQuery db q2))
+    print (rowsOf (runStatement db q2))
 
     let q3 = makeSelect ["name"] "nonexistent" Nothing
-    print (rowsOf (runQuery db q3))
+    print (rowsOf (runStatement db q3))
 
     let q4 =
             makeSelect
@@ -57,17 +60,16 @@ main = do
                         (Gt (Col "age") (LitInt 30))
                     )
                 )
-    print (rowsOf (runQuery db q4))
+    print (rowsOf (runStatement db q4))
 
-    -- 解析 SQL 文本，再交给执行引擎
-    let parsed = parseQuery "SELECT name FROM users WHERE age > 18 AND name = 'Alice'"
-    print (rowsOf (parsed >>= runQuery db))
+    let parsed = parseStatement "SELECT name FROM users WHERE age > 18 AND name = 'Alice'"
+    print (rowsOf (parsed >>= runStatement db))
 
     putStrLn "\n==================== Optimizer ====================="
     let planSql =
             "SELECT u.name, o.product FROM users u \
             \JOIN orders o ON u.id = o.user_id WHERE u.age > 18"
-    case parseQuery planSql of
+    case parseStatement planSql of
         Left err -> putStrLn err
         Right query -> case translate query of
             Left err -> putStrLn err
@@ -77,4 +79,4 @@ main = do
                 putStrLn "--- plan after optimization ---"
                 putStrLn (renderPlan (optimize db plan))
                 putStrLn "--- rows ---"
-                print (rowsOf (runQuery db query))
+                print (rowsOf (runStatement db query))
diff --git a/chusql-engine/src/ChuSQL/Algebra/Eval.hs b/chusql-engine/src/ChuSQL/Algebra/Eval.hs
index 7875913..714a309 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Eval.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Eval.hs
@@ -8,29 +8,31 @@ import ChuSQL.Storage (MonadStorage (..))
 import ChuSQL.Syntax.AST (Expr (..))
 import Control.Monad (filterM)
 
--- 执行：按关系算子树真正算出结果行（Scan 阶段会给列名加上别名前缀）。
+-- 执行：按算子树算出结果行（Scan 阶段会加别名前缀）。
 
--- 投影：只保留清单里的列；哨兵 "*" 表示全部列。
+-- * 工具
+-- | 只保留清单里的列
 project :: [String] -> Row -> Row
 project ["*"] row = row
 project cs row = [(c, v) | (c, v) <- row, c `elem` cs]
 
--- 给一行里的每个列名加上别名前缀（如 "u."）。
+-- | 给列名加别名前缀
 addPrefix :: String -> Row -> Row
 addPrefix prefix = map (\(k, v) -> (prefix ++ k, v))
 
--- 索引查找的约定：主键列名是 "id"（优化器只在这种情况下才把过滤改写成 Lookup）。
+-- | 主键匹配条件（id = k）
 keyCondition :: Int -> Expr
 keyCondition k = Eq (Col "id") (LitInt k)
 
--- 扫描一张表；有别名就给每个列名加上前缀，JOIN 两边同名列靠它区分。
+-- | 扫描一张表
 evalScan :: Database -> Maybe String -> String -> Either String [Row]
 evalScan db mAlias tbl = do
     table <- lookupTable db tbl
     let prefix = maybe "" (++ ".") mAlias
     Right (map (addPrefix prefix) (tableRows table))
 
--- 执行关系代数运算：Scan / Lookup / Filter / Project / Sort / Limit / Join 各一支。
+-- * 求值
+-- | 纯求值（不需要存储）
 evalRelOp :: Database -> RelOp -> Either String [Row]
 evalRelOp db (Scan mAlias tbl) = evalScan db mAlias tbl
 evalRelOp db (Lookup tbl k) = do
@@ -51,18 +53,18 @@ evalRelOp db (Limit n op) = do
 evalRelOp db (Join left right cond) = do
     lrows <- evalRelOp db left
     rrows <- evalRelOp db right
-    let cross = [l ++ r | l <- lrows, r <- rrows] -- 笛卡尔积
+    let cross = [l ++ r | l <- lrows, r <- rrows]
     filterM (evalCondForRow cond) cross
 
--- | Monadic 版本：Lookup 直接问存储要一行（走索引），其余算子照原样递归。
+-- | 单子求值：Lookup 问存储
 evalRelOpM :: (MonadStorage m) => Database -> RelOp -> m (Either String [Row])
+evalRelOpM db (Scan a t) = pure (evalScan db a t)
 evalRelOpM _ (Lookup t k) = do
     result <- lookupByKey t k
     pure $ case result of
         Left e -> Left e
         Right Nothing -> Right []
         Right (Just r) -> Right [r]
-evalRelOpM db (Scan a t) = pure (evalScan db a t)
 evalRelOpM db (Filter p x) = do
     result <- evalRelOpM db x
     pure $ do
diff --git a/chusql-engine/src/ChuSQL/Algebra/Expr.hs b/chusql-engine/src/ChuSQL/Algebra/Expr.hs
index a47cbdf..c4533aa 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Expr.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Expr.hs
@@ -4,9 +4,10 @@ import ChuSQL.Model
 import ChuSQL.Syntax.AST
 import Control.Monad (join)
 
--- 表达式求值：在一行（列名 → 值）上算出单个值；另外提供"静态收集表达式里用到哪些列"的工具。
+-- 表达式求值：拿一行数据算出一个值。
 
--- 表达式求值
+-- * 求值
+-- | 在一行上求出表达式的值
 evalExpr :: Expr -> Row -> Either String Value
 evalExpr (Col name) row =
     maybe (Left ("unknown column: " ++ name)) Right (lookup name row)
@@ -19,7 +20,8 @@ evalExpr (Eq a b) row = liftBinOp eqOp a b row
 evalExpr (And a b) row = liftBinOp (boolOp (&&)) a b row
 evalExpr (Or a b) row = liftBinOp (boolOp (||)) a b row
 
--- 收集表达式里用到的列名
+-- * 列引用
+-- | 表达式用到了哪些列
 colsInExpr :: Expr -> [String]
 colsInExpr (Col c) = [c]
 colsInExpr (Gt a b) = colsInExpr a ++ colsInExpr b
@@ -29,7 +31,7 @@ colsInExpr (And a b) = colsInExpr a ++ colsInExpr b
 colsInExpr (Or a b) = colsInExpr a ++ colsInExpr b
 colsInExpr _ = []
 
--- 对行计算条件语句
+-- | 判断条件真假
 evalCondForRow :: Expr -> Row -> Either String Bool
 evalCondForRow e row = do
     v <- evalExpr e row
@@ -37,7 +39,8 @@ evalCondForRow e row = do
         VBool b -> Right b
         _ -> Left "type error: WHERE condition must be a boolean"
 
--- 固定模式：对两个子表达式求值，并返还给二元操作符
+-- * 内部
+-- | 把二元运算提升到 Either
 liftBinOp ::
     (Value -> Value -> Either String Value) ->
     Expr ->
@@ -46,16 +49,16 @@ liftBinOp ::
     Either String Value
 liftBinOp f a b row = join (f <$> evalExpr a row <*> evalExpr b row)
 
--- 整数比较
+-- | 整数二元运算
 intOp :: (Int -> Int -> Bool) -> Value -> Value -> Either String Value
 intOp f (VInt x) (VInt y) = Right (VBool (f x y))
 intOp _ _ _ = Left "type error: expected two integers"
 
--- 布尔运算
+-- | 布尔二元运算
 boolOp :: (Bool -> Bool -> Bool) -> Value -> Value -> Either String Value
 boolOp f (VBool x) (VBool y) = Right (VBool (f x y))
 boolOp _ _ _ = Left "type error: expected two booleans"
 
--- 相等比较
+-- | 相等比较
 eqOp :: Value -> Value -> Either String Value
 eqOp x y = Right (VBool (x == y))
diff --git a/chusql-engine/src/ChuSQL/Algebra/Op.hs b/chusql-engine/src/ChuSQL/Algebra/Op.hs
index bf4ab50..b5bd289 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Op.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Op.hs
@@ -2,9 +2,9 @@ module ChuSQL.Algebra.Op (RelOp (..), renderPlan) where
 
 import ChuSQL.Syntax.AST (Expr, SortDir)
 
--- 关系代数算子：执行计划用 RelOp 表示；另外提供一个把计划打印成缩进文本的辅助函数。
+-- 关系代数算子，以及把算子树渲染成文本。
 
--- 关系代数算子
+-- | 算子树的一个节点
 data RelOp
     = Scan (Maybe String) String
     | Lookup String Int
@@ -15,13 +15,13 @@ data RelOp
     | Join RelOp RelOp Expr
     deriving (Show, Eq)
 
--- 把算子树画成缩进文本（演示和调试用）
+-- | 渲染成缩进文本
 renderPlan :: RelOp -> String
 renderPlan = go 0
   where
     go ind op = case op of
-        Lookup t k -> "Lookup " ++ show t ++ " " ++ show k
         Scan a t -> pad ++ "Scan " ++ show a ++ " " ++ show t
+        Lookup t k -> pad ++ "Lookup " ++ show t ++ " " ++ show k
         Filter e x -> pad ++ "Filter " ++ show e ++ "\n" ++ go (ind + 1) x
         Project c x -> pad ++ "Project " ++ show c ++ "\n" ++ go (ind + 1) x
         Sort s x -> pad ++ "Sort " ++ show s ++ "\n" ++ go (ind + 1) x
diff --git a/chusql-engine/src/ChuSQL/Algebra/Optimize.hs b/chusql-engine/src/ChuSQL/Algebra/Optimize.hs
index 76d4516..9033b36 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Optimize.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Optimize.hs
@@ -5,42 +5,41 @@ import ChuSQL.Algebra.Op (RelOp (..))
 import ChuSQL.Model
 import ChuSQL.Syntax.AST (Expr (..))
 
--- 查询优化：谓词下推 + 投影下推 + 常量折叠，反复应用规则直到算子树形状不再变化。
+-- 查询优化：谓词下推 + 投影下推 + 常量折叠，跑到不动点。
 
 -- * 谓词下推
-
--- | 一个算子会产出哪些列；返回 ["*"] 表示"全部列，不用挑"
+-- | 算子会产出哪些列
 relOpCols :: Database -> RelOp -> [String]
-relOpCols db (Filter _ x) = relOpCols db x
-relOpCols db (Sort _ x) = relOpCols db x
-relOpCols db (Limit _ x) = relOpCols db x
-relOpCols _ (Project ["*"] _) = ["*"]
-relOpCols _ (Project cols _) = cols
-relOpCols db (Join l r _) = relOpCols db l ++ relOpCols db r
-relOpCols db (Lookup tbl _) = relOpCols db (Scan Nothing tbl)
 relOpCols db (Scan mAlias tbl) =
     case lookup tbl db of
         Nothing -> []
         Just t -> map (prefix ++) (colNames t)
   where
     prefix = maybe "" (++ ".") mAlias
+relOpCols db (Lookup tbl _) = relOpCols db (Scan Nothing tbl)
+relOpCols db (Filter _ x) = relOpCols db x
+relOpCols _ (Project ["*"] _) = ["*"]
+relOpCols _ (Project cols _) = cols
+relOpCols db (Sort _ x) = relOpCols db x
+relOpCols db (Limit _ x) = relOpCols db x
+relOpCols db (Join l r _) = relOpCols db l ++ relOpCols db r
 
--- | need 里的列是不是都能在 have 里找到；have 为 ["*"] 时一律为真
+-- | need 是否都在 have 里
 isSubsetOf :: [String] -> [String] -> Bool
 isSubsetOf _ ["*"] = True
 isSubsetOf need have = all (`elem` have) need
 
--- | 把一个用 AND 串起来的条件拆成清单：a AND b AND c 变成 [a, b, c]
+-- | 把 AND 链拆成清单
 splitConj :: Expr -> [Expr]
 splitConj (And a b) = splitConj a ++ splitConj b
 splitConj e = [e]
 
--- | 反过来：把条件清单用 AND 重新串成一个；空清单表示"没有条件"，返回 Nothing
+-- | 把条件清单用 AND 串起来
 combineConj :: [Expr] -> Maybe Expr
 combineConj [] = Nothing
 combineConj (e : es) = Just (foldl And e es)
 
--- | 把条件按"只用到哪一边的列"分成两堆：能下推过去的 / 必须留在原地的
+-- | 条件按列归属分两边
 partitionPred :: [String] -> [Expr] -> ([Expr], [Expr])
 partitionPred have = foldr pick ([], [])
   where
@@ -48,12 +47,12 @@ partitionPred have = foldr pick ([], [])
         | colsInExpr e `isSubsetOf` have = (e : yes, no)
         | otherwise = (yes, e : no)
 
--- | 把一组条件依次套到算子上，一个条件一层 Filter
+-- | 依次套上若干 Filter
 applyFilters :: [Expr] -> RelOp -> RelOp
 applyFilters [] op = op
 applyFilters (e : es) op = applyFilters es (Filter e op)
 
--- | Filter 压在 Join 上时的下推规则：条件按列归属拆到左右两侧，跨两边的才留在 Join 上方
+-- | Filter 压在 Join 上时下推
 pushJoin :: Database -> Expr -> RelOp -> RelOp -> Expr -> RelOp
 pushJoin db p l r c =
     let preds = splitConj p
@@ -68,26 +67,26 @@ pushJoin db p l r c =
             Nothing -> joined
             Just p' -> Filter p' joined
 
--- | Filter 压在 Filter / Sort 上时的下推规则：合并上下两层 Filter，或把 Filter 挪到 Sort 下面
+-- | 合并两层 Filter 或挪到 Sort 下
 pushOne :: Database -> RelOp -> RelOp
 pushOne _ (Filter p (Filter q x)) = Filter (And p q) x
 pushOne _ (Filter p (Sort spec x)) = Sort spec (Filter p x)
 pushOne _ op = op
 
--- * 投影下推
 
--- | 是不是要拿全部列（need 里含哨兵 "*"）。
+-- * 投影下推
+-- | 是否要全部列
 needsAll :: [String] -> Bool
 needsAll = elem allColumns
 
--- | 叶子算子（扫描 / 索引查找）的投影下推：需要全部列就原样保留，缺列才套一层 Project
+-- | 叶子算子的投影下推
 pushProjectLeaf :: Database -> [String] -> RelOp -> RelOp
 pushProjectLeaf db need leaf
     | needsAll need = leaf
     | all (`elem` need) (relOpCols db leaf) = leaf
     | otherwise = Project need leaf
 
--- | 投影下推：把"上层需要哪些列"一路往下传，JOIN 两侧各自只保留自己需要的列。
+-- | 把需要哪些列往下传
 pushProject :: Database -> [String] -> RelOp -> RelOp
 pushProject db _ (Project cols x) = case pushProject db cols x of
     Project cols' y | cols' == cols -> Project cols y
@@ -107,9 +106,9 @@ pushProject db need (Join l r c)
 pushProject db need leaf@(Scan _ _) = pushProjectLeaf db need leaf
 pushProject db need leaf@(Lookup _ _) = pushProjectLeaf db need leaf
 
--- * 常量折叠
 
--- | 折一个表达式：不含列就直接求值替换成字面量，含列或求值失败则原样返回
+-- * 常量折叠
+-- | 折一个表达式节点
 foldNode :: Expr -> Expr
 foldNode e
     | null (colsInExpr e) = case evalExpr e [] of
@@ -119,7 +118,7 @@ foldNode e
         Left _ -> e
     | otherwise = e
 
--- | 自底向上折叠整个表达式：先把子表达式折干净，再折自己
+-- | 自底向上折整棵表达式
 foldConstants :: Expr -> Expr
 foldConstants (Gt a b) = foldNode (Gt (foldConstants a) (foldConstants b))
 foldConstants (Lt a b) = foldNode (Lt (foldConstants a) (foldConstants b))
@@ -128,9 +127,9 @@ foldConstants (And a b) = foldNode (And (foldConstants a) (foldConstants b))
 foldConstants (Or a b) = foldNode (Or (foldConstants a) (foldConstants b))
 foldConstants e = e
 
--- * 执行优化
 
--- | 单节点重写：把 Filter 分派给上面几条规则，另外负责恒真条件删除与恒等投影消除
+-- * 执行优化
+-- | 单节点重写
 rewriteNode :: Database -> RelOp -> RelOp
 rewriteNode _ (Filter (Eq (Col k) (LitInt v)) (Scan _ t))
     | k == "id" = Lookup t v
@@ -141,7 +140,7 @@ rewriteNode db (Filter p x) = case foldConstants p of
 rewriteNode _ (Project ["*"] x) = x
 rewriteNode db op = pushOne db op
 
--- | 自底向上遍历整棵算子树，每个节点套一次 rewriteNode
+-- | 自底向上遍历一次
 optimizeRelOp :: Database -> RelOp -> RelOp
 optimizeRelOp db = rewriteNode db . descend
   where
@@ -152,12 +151,12 @@ optimizeRelOp db = rewriteNode db . descend
     descend (Join l r c) = Join (optimizeRelOp db l) (optimizeRelOp db r) c
     descend x = x
 
--- | 谓词下推 + 常量折叠：反复应用规则，直到算子树的形状不再变化（到不动点为止）
+-- | 反复跑到不动点
 optimizePredicates :: Database -> RelOp -> RelOp
 optimizePredicates db op =
     let op' = optimizeRelOp db op
      in if op' == op then op else optimizePredicates db op'
 
--- | 优化器总入口：先把谓词下推与常量折叠跑到不动点，再做一次投影下推
+-- | 优化总入口
 optimize :: Database -> RelOp -> RelOp
 optimize db op = pushProject db ["*"] (optimizePredicates db op)
diff --git a/chusql-engine/src/ChuSQL/Algebra/Planner.hs b/chusql-engine/src/ChuSQL/Algebra/Planner.hs
index 909cd4b..404bab0 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Planner.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Planner.hs
@@ -3,16 +3,16 @@ module ChuSQL.Algebra.Planner (translate) where
 import ChuSQL.Algebra.Op
 import ChuSQL.Syntax.AST
 
--- 计划翻译：把 AST 里的 SELECT 翻译成关系代数算子树（只翻译，不做合法性检查）。
+-- 计划生成：把语句翻译成算子树。
 
--- 把 FROM 从句转成 Scan / Join 算子。
+-- | 把 FROM 子句翻成 Scan / Join
 fromToRelOp :: FromClause -> RelOp
 fromToRelOp (FromTable mAlias tbl) = Scan mAlias tbl
 fromToRelOp (FromJoin left mAlias tbl cond) =
     Join (fromToRelOp left) (Scan mAlias tbl) cond
 
--- 翻译入口：把 SELECT 翻译成算子树；其它语句类型不支持（返回 Left）。
-translate :: Query -> Either String RelOp
+-- | 翻成：过滤 -> 排序 -> 截断 -> 取列
+translate :: Statement -> Either String RelOp
 translate q = case q of
     Select
         { selectCols = cols
diff --git a/chusql-engine/src/ChuSQL/Algebra/Sort.hs b/chusql-engine/src/ChuSQL/Algebra/Sort.hs
index 1d9c471..0dbb3a0 100644
--- a/chusql-engine/src/ChuSQL/Algebra/Sort.hs
+++ b/chusql-engine/src/ChuSQL/Algebra/Sort.hs
@@ -4,22 +4,22 @@ import ChuSQL.Model
 import ChuSQL.Syntax.AST
 import Data.List (sortBy)
 
--- 排序：按 ORDER BY 的列清单逐列比较（支持 ASC / DESC），供执行 Sort 算子时使用。
+-- 排序：按多列排序，每列可升可降。
 
--- 反向排序
+-- | 反转比较结果
 flipOrdering :: Ordering -> Ordering
 flipOrdering LT = GT
 flipOrdering GT = LT
 flipOrdering EQ = EQ
 
--- 定义值的比较规则
+-- | 比较两个值
 compareValue :: Value -> Value -> Ordering
 compareValue (VInt a) (VInt b) = compare a b
 compareValue (VStr a) (VStr b) = compare a b
 compareValue (VBool a) (VBool b) = compare a b
 compareValue _ _ = EQ
 
--- 定义行的比较规则
+-- | 按排序要求比较两行
 compareRows :: [(String, SortDir)] -> Row -> Row -> Ordering
 compareRows [] _ _ = EQ
 compareRows ((col, dir) : rest) r1 r2 =
@@ -33,7 +33,7 @@ compareRows ((col, dir) : rest) r1 r2 =
                         else o
         _ -> compareRows rest r1 r2
 
--- 将表的每行排序
+-- | 排序若干行
 sortRows :: [(String, SortDir)] -> [Row] -> [Row]
 sortRows [] rows = rows
 sortRows spec rows = sortBy (compareRows spec) rows
diff --git a/chusql-engine/src/ChuSQL/Engine.hs b/chusql-engine/src/ChuSQL/Engine.hs
index 8215b18..03caff6 100644
--- a/chusql-engine/src/ChuSQL/Engine.hs
+++ b/chusql-engine/src/ChuSQL/Engine.hs
@@ -1,4 +1,4 @@
-module ChuSQL.Engine (runQuery, runQueryM, rowsOf) where
+module ChuSQL.Engine (runStatement, runStatementM, rowsOf) where
 
 import ChuSQL.Algebra.Eval (evalRelOpM)
 import ChuSQL.Algebra.Expr (evalCondForRow, evalExpr)
@@ -11,37 +11,39 @@ import ChuSQL.Storage.Memory (MemoryStorage (runMemoryStorage))
 import ChuSQL.Syntax.AST
 import Control.Monad (filterM)
 
--- | 对外入口：签名不变，内部走内存实现。
-runQuery :: Database -> Query -> Either String (Database, [Row])
-runQuery db q = do
-    (result, db') <- runMemoryStorage (runQueryM q) db
+-- 引擎入口：语义检查 + 分发执行，以及内存实现与泛型版本。
+
+-- * 对外入口
+-- | 跑一条语句（内存实现）
+runStatement :: Database -> Statement -> Either String (Database, [Row])
+runStatement db q = do
+    (result, db') <- runMemoryStorage (runStatementM q) db
     rows <- result
     Right (db', rows)
 
--- | 只要结果行（丢掉更新后的数据库），给演示和测试用。
+-- | 只要结果行
 rowsOf :: Either String (Database, [Row]) -> Either String [Row]
 rowsOf = fmap snd
 
--- * 泛型入口：走 MonadStorage，未来 IPCStorage 复用同一份代码
 
--- | 语义检查 + 分发到具体语句。
-runQueryM :: (MonadStorage m) => Query -> m (Either String [Row])
-runQueryM q = do
+-- | 泛型入口：先检查再执行
+runStatementM :: (MonadStorage m) => Statement -> m (Either String [Row])
+runStatementM q = do
     db <- snapshot
     case check db q of
         Left err -> pure (Left err)
-        Right _ -> runQueryUncheckedM q
+        Right _ -> runStatementUncheckedM q
 
--- | SELECT：拿快照，跑 translate → optimize → evalRelOp。
-runQueryUncheckedM :: (MonadStorage m) => Query -> m (Either String [Row])
-runQueryUncheckedM q@Select{} = do
+-- * 分发执行
+-- | 按语句类型分发（已检查过）
+runStatementUncheckedM :: (MonadStorage m) => Statement -> m (Either String [Row])
+runStatementUncheckedM q@Select{} = do
     db <- snapshot
     case translate q of
         Left e -> pure (Left e)
         Right relOp -> evalRelOpM db (optimize db relOp)
 
--- \| INSERT：求值后追加一行。
-runQueryUncheckedM (Insert tbl cols vals) =
+runStatementUncheckedM (Insert tbl cols vals) =
     case mapM (\e -> evalExpr e []) vals of
         Left err -> pure (Left err)
         Right values
@@ -51,8 +53,7 @@ runQueryUncheckedM (Insert tbl cols vals) =
                 result <- insert tbl (zip cols values)
                 pure (result >> Right [])
 
--- \| DELETE：扫表、筛掉命中行、整体写回。
-runQueryUncheckedM (Delete tbl mWhere) = do
+runStatementUncheckedM (Delete tbl mWhere) = do
     rowsResult <- scan tbl
     case rowsResult of
         Left err -> pure (Left err)
@@ -66,12 +67,11 @@ runQueryUncheckedM (Delete tbl mWhere) = do
                     result <- replaceAll tbl keptRows
                     pure (result >> Right [])
   where
-    -- \| 保留 = 条件不成立。
+    -- \| 保留 = 条件不成立
     shouldKeep :: Expr -> Row -> Either String Bool
     shouldKeep e row = not <$> evalCondForRow e row
 
--- \| UPDATE：扫表、逐行改、整体写回。
-runQueryUncheckedM (Update tbl assigns mWhere) = do
+runStatementUncheckedM (Update tbl assigns mWhere) = do
     rowsResult <- scan tbl
     case rowsResult of
         Left err -> pure (Left err)
@@ -83,7 +83,7 @@ runQueryUncheckedM (Update tbl assigns mWhere) = do
                     result <- replaceAll tbl rs
                     pure (result >> Right [])
   where
-    -- \| 命中条件就套用赋值，否则原样返回。
+    -- \| 命中条件就套用赋值
     updateRow :: Maybe Expr -> [(String, Expr)] -> Row -> Either String Row
     updateRow cond asgns row = do
         keep <- case cond of
@@ -91,7 +91,15 @@ runQueryUncheckedM (Update tbl assigns mWhere) = do
             Just e -> evalCondForRow e row
         if keep then applyUpdates asgns row else Right row
 
--- | 按 assignments 依次求值并覆盖对应列。
+runStatementUncheckedM (CreateTable name cols) = do
+    result <- createTable name cols
+    pure (result >> Right [])
+runStatementUncheckedM (DropTable name) = do
+    result <- dropTable name
+    pure (result >> Right [])
+
+-- * 更新辅助
+-- | 依次求值并覆盖列
 applyUpdates :: [(String, Expr)] -> Row -> Either String Row
 applyUpdates [] row = Right row
 applyUpdates ((col, e) : rest) row = do
diff --git a/chusql-engine/src/ChuSQL/Model.hs b/chusql-engine/src/ChuSQL/Model.hs
index 0d0be17..6f6de07 100644
--- a/chusql-engine/src/ChuSQL/Model.hs
+++ b/chusql-engine/src/ChuSQL/Model.hs
@@ -1,25 +1,26 @@
 module ChuSQL.Model (Column (..), Value (..), Row, Table (..), Database, colNames, colType, lookupTable, allColumns) where
 
--- 数据模型：列类型、值、行、表、数据库，外加"按名查表 / 查列类型"这类通用小工具。
+-- 数据模型：列类型、值、行、表、数据库，外加几个查表小工具。
 
--- 列的类型
+-- * 类型
+-- | 列的类型
 data Column
     = TInt
     | TStr
     | TBool
     deriving (Show, Eq)
 
--- 列的值：整数、字符串、布尔
+-- | 列的值
 data Value
     = VInt Int
     | VStr String
     | VBool Bool
     deriving (Show, Eq)
 
--- 一行：列名 → 值
+-- | 一行：列名 -> 值
 type Row = [(String, Value)]
 
--- 一张表
+-- | 一张表
 data Table = Table
     { tableName :: String
     , tableCols :: [(String, Column)]
@@ -27,21 +28,22 @@ data Table = Table
     }
     deriving (Show)
 
--- 数据库：多张表
+-- | 数据库：多张表
 type Database = [(String, Table)]
 
--- 获取列名
+-- * 工具
+-- | 取表的列名
 colNames :: Table -> [String]
 colNames = map fst . tableCols
 
--- 查某一列的类型
+-- | 查某列的类型
 colType :: Table -> String -> Maybe Column
 colType t c = lookup c (tableCols t)
 
--- 按名字查表；表不存在就报错
+-- | 按名查表，没有就报错
 lookupTable :: Database -> String -> Either String Table
 lookupTable db t = maybe (Left ("unknown table: " ++ t)) Right (lookup t db)
 
--- 投影列清单里的哨兵值：它表示"全部列，不用挑"，不是列名
+-- | 投影哨兵 "*"
 allColumns :: String
 allColumns = "*"
diff --git a/chusql-engine/src/ChuSQL/Semantic.hs b/chusql-engine/src/ChuSQL/Semantic.hs
index d5c5d18..e7cd7fd 100644
--- a/chusql-engine/src/ChuSQL/Semantic.hs
+++ b/chusql-engine/src/ChuSQL/Semantic.hs
@@ -3,19 +3,18 @@ module ChuSQL.Semantic (check) where
 import ChuSQL.Algebra.Expr (colsInExpr)
 import ChuSQL.Model
 import ChuSQL.Syntax.AST
-import Data.List (intercalate)
+import Data.List (intercalate, nub)
 
--- 语义检查：执行前的关卡 —— 表和列存不存在、表达式类型对不对、写入的值类型是否匹配。
+-- 语义检查：表和列在不在、类型对不对，全部在执行前查。
 
--- * 表与列名解析
-
--- | 给一批列加上"别名."前缀
+-- * 环境
+-- | 给列名加上别名前缀
 prefixColumns :: Maybe String -> [(String, Column)] -> [(String, Column)]
 prefixColumns mAlias cols = [(prefix ++ c, ty) | (c, ty) <- cols]
   where
     prefix = maybe "" (++ ".") mAlias
 
--- | 走一遍 FROM：算出可用列（带别名前缀），顺手把每个 ON 条件也查了
+-- | 收集 FROM 能提供的列
 checkFrom :: Database -> FromClause -> Either String [(String, Column)]
 checkFrom db (FromTable mAlias tbl) = do
     t <- lookupTable db tbl
@@ -27,9 +26,9 @@ checkFrom db (FromJoin left mAlias tbl cond) = do
     checkBool "ON" env cond
     Right env
 
--- * 列检查与报错
 
--- | 统一拼一条带"可用列清单"的报错
+-- * 检查
+-- | 拼“列不存在”的报错
 missingColumn :: String -> String -> [(String, Column)] -> String
 missingColumn place c env =
     "unknown column in " ++ place ++ ": " ++ c ++ hint
@@ -38,16 +37,15 @@ missingColumn place c env =
         | null env = ""
         | otherwise = " (available: " ++ intercalate ", " (map fst env) ++ ")"
 
--- | 请求的列必须都在可用清单里；哨兵 allColumns 表示"全部列"，放行
+-- | 检查列是否都在环境里
 checkColumns :: String -> [(String, Column)] -> [String] -> Either String ()
 checkColumns place env requested =
     case [c | c <- requested, c /= allColumns, c `notElem` map fst env] of
         [] -> Right ()
         (c : _) -> Left (missingColumn place c env)
 
--- * 表达式类型推导
 
--- | 推出一个表达式的结果类型；列不存在、或类型对不上，都报错
+-- | 推导表达式的类型
 inferExpr :: String -> [(String, Column)] -> Expr -> Either String Column
 inferExpr place env (Col c) = maybe (Left (missingColumn place c env)) Right (lookup c env)
 inferExpr _ _ (LitInt _) = Right TInt
@@ -64,7 +62,7 @@ inferExpr place env (Eq a b) = do
         then Right TBool
         else Left (place ++ ": both sides of = must have the same type, got " ++ show ta ++ " and " ++ show tb)
 
--- | 二元运算的通用检查：两边都必须是同一种期望类型，结果都是布尔
+-- | 检查二元运算两边的类型
 operands :: String -> [(String, Column)] -> Column -> Expr -> Expr -> Either String Column
 operands place env want a b = do
     ta <- inferExpr place env a
@@ -73,7 +71,7 @@ operands place env want a b = do
         then Right TBool
         else Left (place ++ ": operator needs " ++ show want ++ " on both sides, got " ++ show ta ++ " and " ++ show tb)
 
--- | 这个表达式必须能算成一个条件（布尔）
+-- | 要求条件能算出布尔
 checkBool :: String -> [(String, Column)] -> Expr -> Either String ()
 checkBool place env e = do
     checkColumns place env (colsInExpr e)
@@ -82,9 +80,9 @@ checkBool place env e = do
         then Right ()
         else Left (place ++ ": condition must be a boolean, got " ++ show t)
 
--- * 写入语句
 
--- | 一条赋值的通用检查：目标列必须存在，右边表达式的类型要对得上
+-- * 写入语句
+-- | 检查赋值列和类型
 checkTyped :: String -> [(String, Column)] -> Table -> (String, Expr) -> Either String ()
 checkTyped place env t (c, e) = do
     want <- maybe (Left (missingColumn place c (tableCols t))) Right (colType t c)
@@ -93,18 +91,18 @@ checkTyped place env t (c, e) = do
         then Right ()
         else Left (place ++ ": column " ++ c ++ " needs " ++ show want ++ ", got " ++ show got)
 
--- | INSERT 的一个值：环境是空的 —— 值必须是字面量，写列名会被拦下
+-- | 检查插入值的类型
 checkValue :: Table -> (String, Expr) -> Either String ()
 checkValue = checkTyped "INSERT" []
 
--- | UPDATE 的一个赋值：环境是整张表 —— 右边可以引用本行的列
+-- | 检查 UPDATE 的赋值
 checkAssign :: Table -> (String, Expr) -> Either String ()
 checkAssign t = checkTyped "UPDATE" (tableCols t) t
 
--- * 总入口
 
--- | 语义检查总入口：合法返回 Right ()，不合法返回 Left（带人话解释）
-check :: Database -> Query -> Either String ()
+-- * 入口
+-- | 按语句类型分派检查
+check :: Database -> Statement -> Either String ()
 check db q = case q of
     Select
         { selectCols = cols
@@ -128,3 +126,15 @@ check db q = case q of
         checkColumns "UPDATE" (tableCols t) (map fst assigns)
         mapM_ (checkAssign t) assigns
         mapM_ (checkBool "WHERE" (tableCols t)) mWhere
+    CreateTable name cols -> do
+        if null name
+            then Left "CREATE TABLE: empty table name"
+            else do
+                let names = map fst cols
+                if length names /= length (nub names)
+                    then Left ("CREATE TABLE: duplicate column names in " ++ name)
+                    else Right ()
+    DropTable name ->
+        if null name
+            then Left "DROP TABLE: empty table name"
+            else Right ()
diff --git a/chusql-engine/src/ChuSQL/Storage.hs b/chusql-engine/src/ChuSQL/Storage.hs
index 87435bd..8ee9a26 100644
--- a/chusql-engine/src/ChuSQL/Storage.hs
+++ b/chusql-engine/src/ChuSQL/Storage.hs
@@ -1,20 +1,30 @@
-module ChuSQL.Storage (MonadStorage (..)) where
+module ChuSQL.Storage (
+    MonadStorage (..),
+) where
 
-import ChuSQL.Model (Database, Row)
+import ChuSQL.Model (Column, Database, Row)
 
--- 存储层抽象：上层只认 domain 类型，不关心底层是内存还是 IPC。
+-- 存储层抽象：上层只认 domain 类型，不关心底层实现。
+
+-- | 存储接口：读写表、按主键取行、取快照
 class (Monad m) => MonadStorage m where
-    -- 全表扫描；表不存在返回 Left。
+    -- \| 全表扫描
     scan :: String -> m (Either String [Row])
 
-    -- 追加一行到表尾；表不存在返回 Left。
+    -- \| 追加一行
     insert :: String -> Row -> m (Either String ())
 
-    -- 用新行列表整体替换一张表。
+    -- \| 整表替换
     replaceAll :: String -> [Row] -> m (Either String ())
 
-    -- 按主键查一行；命中返回 Just，未命中返回 Nothing。
+    -- \| 按主键取一行
     lookupByKey :: String -> Int -> m (Either String (Maybe Row))
 
-    -- 取全库快照，喂给还接收 Database 的语义检查 / 优化器 / evalRelOp。
+    -- \| 建一张空表
+    createTable :: String -> [(String, Column)] -> m (Either String ())
+
+    -- \| 删除表
+    dropTable :: String -> m (Either String ())
+
+    -- \| 取全库快照
     snapshot :: m Database
diff --git a/chusql-engine/src/ChuSQL/Storage/IPC.hs b/chusql-engine/src/ChuSQL/Storage/IPC.hs
index 3a89c41..facf87c 100644
--- a/chusql-engine/src/ChuSQL/Storage/IPC.hs
+++ b/chusql-engine/src/ChuSQL/Storage/IPC.hs
@@ -11,11 +11,13 @@ module ChuSQL.Storage.IPC (
     doLookupByKey,
     doInsertKeyed,
     doDescribeTable,
+    doCreateTable,
+    doDropTable,
 ) where
 
 import ChuSQL.Model
 import ChuSQL.Storage
-import Control.Exception (bracket)
+import Control.Exception (IOException, bracket, try)
 import Data.Aeson (FromJSON (..), ToJSON (..), eitherDecodeStrict, encode, object, withObject, (.:), (.=))
 import Data.Aeson qualified as A
 import Data.Aeson.Key qualified as K
@@ -29,39 +31,41 @@ import Data.Text qualified as T
 import System.Environment (lookupEnv)
 import System.IO
 
--- IPC 存储实现：每个 MonadStorage 方法翻译成管道上的一条 JSON 请求。
+-- IPC 存储实现：每个存储方法翻成管道上的一条 JSON 请求。
 
--- | IPC 实现：通过命名管道连 Rust 存储进程。
+-- * 存储实现
+-- | 命名管道上的存储
 newtype IPCStorage a = IPCStorage
     { runIPCStorage :: IO a
     }
 
--- | Functor：把 fmap 转发给底下的 IO。
+-- | Functor：转发给 IO
 instance Functor IPCStorage where
     fmap f (IPCStorage m) = IPCStorage (fmap f m)
 
--- | Applicative：把 pure / <*> 转发给底下的 IO。
+-- | Applicative：转发给 IO
 instance Applicative IPCStorage where
     pure = IPCStorage . pure
     IPCStorage mf <*> IPCStorage ma = IPCStorage (mf <*> ma)
 
--- | Monad：顺序执行，转发给底下的 IO。
+-- | Monad：顺序执行
 instance Monad IPCStorage where
     IPCStorage m >>= k = IPCStorage $ do
         a <- m
         runIPCStorage (k a)
 
--- | 管道路径；默认 \\.\pipe\chusql-storage，可用 CHUSQL_PIPE 覆盖。
+-- * 管道
+-- | 管道路径
 pipePath :: IO String
 pipePath = do
     name <- maybe "chusql-storage" id <$> lookupEnv "CHUSQL_PIPE"
     pure ("\\\\.\\pipe\\" ++ name)
 
--- | 打开管道、跑闭包、关闭。
+-- | 开管道跑闭包
 withPipe :: (Handle -> IO a) -> IO a
 withPipe = bracket openPipe hClose
   where
-    -- \| 二进制读写、不做换行翻译，跟 Rust 侧对齐。
+    -- \| 打开管道句柄
     openPipe = do
         path <- pipePath
         h <- openFile path ReadWriteMode
@@ -69,39 +73,46 @@ withPipe = bracket openPipe hClose
         hSetNewlineMode h noNewlineTranslation
         pure h
 
--- | 发一条请求，读一条响应。
+-- | 发一条请求读一条响应
 sendRequest :: Request -> IO Response
-sendRequest req = withPipe $ \h -> do
-    BL.hPutStr h (encode req)
-    BSC.hPutStr h "\n"
-    hFlush h
-    line <- BSC.hGetLine h
-    let cleaned = BSC.dropWhileEnd (== '\r') line
-    case eitherDecodeStrict cleaned of
-        Left err -> pure (RespError ("decode: " ++ err))
-        Right r -> pure r
+sendRequest req = do
+    result <- try (withPipe roundTrip) :: IO (Either IOException Response)
+    pure $ case result of
+        Left e -> RespError ("pipe error: " ++ show e)
+        Right r -> r
+  where
+    roundTrip h = do
+        BL.hPutStr h (encode req)
+        BSC.hPutStr h "\n"
+        hFlush h
+        line <- BSC.hGetLine h
+        let cleaned = BSC.dropWhileEnd (== '\r') line
+        case eitherDecodeStrict cleaned of
+            Left err -> pure (RespError ("decode: " ++ err))
+            Right r -> pure r
 
--- * JSON 编解码
 
--- | 一列的 schema；对应 Rust 侧的 SchemaColumn。
+-- * 编解码
+-- | 一列的 schema
 data SchemaColumn = SchemaColumn
     { scName :: String
     , scType :: String
     }
     deriving (Show, Eq)
 
--- | SchemaColumn 编码；Haskell 侧只发 DescribeTable，编码用不上，暂存实现。
+-- | SchemaColumn 编码
 instance ToJSON SchemaColumn where
     toJSON (SchemaColumn n t) = object ["name" .= n, "ty" .= t]
 
--- | SchemaColumn 解码：从 {"name": "...", "ty": "int"|"str"|"bool"} 读回。
+-- | SchemaColumn 解码
 instance FromJSON SchemaColumn where
     parseJSON = withObject "SchemaColumn" $ \o -> do
         n <- o .: "name"
         t <- o .: "ty"
         pure (SchemaColumn n t)
 
--- | 请求；对应 Rust 侧带 method tag 的 enum。
+-- * 请求
+-- | 请求类型
 data Request
     = ReqPing
     | ReqScan String
@@ -110,8 +121,10 @@ data Request
     | ReqListTables
     | ReqLookupByKey String Int
     | ReqDescribeTable String
+    | ReqCreateTable String [SchemaColumn]
+    | ReqDropTable String
 
--- | 请求编码：method 字段 + 各自参数。
+-- | 请求编码
 instance ToJSON Request where
     toJSON ReqPing = object ["method" .= ("ping" :: T.Text)]
     toJSON (ReqScan t) = object ["method" .= ("scan" :: T.Text), "table" .= t]
@@ -142,17 +155,26 @@ instance ToJSON Request where
             [ "method" .= ("describe_table" :: T.Text)
             , "table" .= t
             ]
+    toJSON (ReqCreateTable t cols) =
+        object
+            [ "method" .= ("create_table" :: T.Text)
+            , "table" .= t
+            , "columns" .= cols
+            ]
+    toJSON (ReqDropTable t) =
+        object ["method" .= ("drop_table" :: T.Text), "table" .= t]
 
--- | 响应；对应 Rust 侧带 status tag 的 enum。
+
+-- | 响应类型
 data Response
     = RespPong
     | RespRows [Row]
     | RespTables [String]
-    | RespSchema [SchemaColumn]
+    | RespSchema [SchemaColumn] Int
     | RespOk
     | RespError String
 
--- | 响应解码：按 status 字段分派。
+-- | 响应解码
 instance FromJSON Response where
     parseJSON = withObject "Response" $ \o -> do
         status <- o .: "status"
@@ -161,17 +183,20 @@ instance FromJSON Response where
             "ok" -> pure RespOk
             "rows" -> RespRows <$> (o .: "rows" >>= mapM rowFromJSON)
             "tables" -> RespTables <$> o .: "tables"
-            "schema" -> RespSchema <$> o .: "columns"
             "error" -> RespError <$> o .: "message"
+            "schema" -> do
+                cols <- o .: "columns"
+                cnt <- o .: "row_count"
+                pure (RespSchema cols cnt)
             other -> fail ("unknown status: " ++ T.unpack other)
 
--- | Value 编码成 JSON 的 number / string / bool。
+-- | 值编码成 JSON
 valueToJSON :: Value -> A.Value
 valueToJSON (VInt n) = A.Number (fromIntegral n)
 valueToJSON (VStr s) = A.String (T.pack s)
 valueToJSON (VBool b) = A.Bool b
 
--- | JSON 解回 Value；number 只接受整数。
+-- | JSON 解回值
 valueFromJSON :: A.Value -> Parser Value
 valueFromJSON (A.Number n) =
     case floatingOrInteger n :: Either Double Integer of
@@ -181,24 +206,24 @@ valueFromJSON (A.String s) = pure (VStr (T.unpack s))
 valueFromJSON (A.Bool b) = pure (VBool b)
 valueFromJSON _ = fail "unsupported value type"
 
--- | 一行编成 JSON object。
+-- | 一行编码成 JSON
 rowToJSON :: Row -> A.Value
 rowToJSON r =
     A.Object (KM.fromList [(K.fromString k, valueToJSON v) | (k, v) <- r])
 
--- | JSON object 解成一行。
+-- | JSON 解回一行
 rowFromJSON :: A.Value -> Parser Row
 rowFromJSON (A.Object o) = mapM toPair (KM.toList o)
   where
-    -- \| 解一个键值对。
+    -- \| 解一个键值对
     toPair (k, v) = do
         val <- valueFromJSON v
         pure (K.toString k, val)
 rowFromJSON _ = fail "row must be a JSON object"
 
--- * 内部请求封装
 
--- | 发 Scan 并把结果取成 Either。
+-- * 内部封装
+-- | 发 Scan
 doScan :: String -> IO (Either String [Row])
 doScan t = do
     resp <- sendRequest (ReqScan t)
@@ -207,16 +232,22 @@ doScan t = do
         RespError e -> Left e
         _ -> Left "unexpected response to scan"
 
--- | 发 Insert（不带索引键）。
+-- | 发 Insert（带 id 键）
 doInsert :: String -> Row -> IO (Either String ())
 doInsert t r = do
-    resp <- sendRequest (ReqInsert t r Nothing)
+    resp <- sendRequest (ReqInsert t r (rowKey r))
     pure $ case resp of
         RespOk -> Right ()
         RespError e -> Left e
         _ -> Left "unexpected response to insert"
 
--- | 发 Insert（带索引键）。
+-- | 取行里的 id 作索引键
+rowKey :: Row -> Maybe Int
+rowKey r = case lookup "id" r of
+    Just (VInt k) -> Just k
+    _ -> Nothing
+
+-- | 发 Insert（指定键）
 doInsertKeyed :: String -> Row -> Int -> IO (Either String ())
 doInsertKeyed t r k = do
     resp <- sendRequest (ReqInsert t r (Just k))
@@ -225,7 +256,7 @@ doInsertKeyed t r k = do
         RespError e -> Left e
         _ -> Left "unexpected response to insert"
 
--- | 发 ReplaceAll。
+-- | 发 ReplaceAll
 doReplaceAll :: String -> [Row] -> IO (Either String ())
 doReplaceAll t rs = do
     resp <- sendRequest (ReqReplaceAll t rs)
@@ -234,7 +265,7 @@ doReplaceAll t rs = do
         RespError e -> Left e
         _ -> Left "unexpected response to replace_all"
 
--- | 发 ListTables。
+-- | 发 ListTables
 doListTables :: IO (Either String [String])
 doListTables = do
     resp <- sendRequest ReqListTables
@@ -243,7 +274,7 @@ doListTables = do
         RespError e -> Left e
         _ -> Left "unexpected response to list_tables"
 
--- | 发 LookupByIndex。
+-- | 发 LookupByIndex
 doLookupByKey :: String -> Int -> IO (Either String (Maybe Row))
 doLookupByKey t k = do
     resp <- sendRequest (ReqLookupByKey t k)
@@ -253,45 +284,63 @@ doLookupByKey t k = do
         RespError e -> Left e
         _ -> Left "unexpected response to lookup_by_index"
 
--- | 发 DescribeTable。
-doDescribeTable :: String -> IO (Either String [SchemaColumn])
+-- | 发 DescribeTable
+doDescribeTable :: String -> IO (Either String ([SchemaColumn], Int))
 doDescribeTable t = do
     resp <- sendRequest (ReqDescribeTable t)
     pure $ case resp of
-        RespSchema cols -> Right cols
+        RespSchema cols n -> Right (cols, n)
         RespError e -> Left e
         _ -> Left "unexpected response to describe_table"
 
--- | 把 Rust 的 schema 列转成 Model 的 Column；未知类型降级为 TStr。
+-- | 发 CreateTable
+doCreateTable :: String -> [SchemaColumn] -> IO (Either String ())
+doCreateTable t cols = do
+    resp <- sendRequest (ReqCreateTable t cols)
+    pure $ case resp of
+        RespOk -> Right ()
+        RespError e -> Left e
+        _ -> Left "unexpected response to create_table"
+
+-- | 发 DropTable
+doDropTable :: String -> IO (Either String ())
+doDropTable t = do
+    resp <- sendRequest (ReqDropTable t)
+    pure $ case resp of
+        RespOk -> Right ()
+        RespError e -> Left e
+        _ -> Left "unexpected response to drop_table"
+
+-- * 表结构
+-- | 线上 schema 转本地列
 schemaToColumns :: [SchemaColumn] -> [(String, Column)]
 schemaToColumns = map go
   where
-    -- \| 按 ty 字符串映射成 Column 构造子。
     go (SchemaColumn n "int") = (n, TInt)
     go (SchemaColumn n "str") = (n, TStr)
     go (SchemaColumn n "bool") = (n, TBool)
     go (SchemaColumn n _) = (n, TStr)
 
--- | 从若干行推断列名与类型；catalog 拿不到时的兜底。
+-- | 从行推断列和类型
 inferColumns :: [Row] -> [(String, Column)]
 inferColumns rows = [(n, inferType n) | n <- names]
   where
-    -- \| 全部出现过的列名。
+    -- \| 出现过的列名
     names = nub (concatMap (map fst) rows)
 
-    -- \| 用第一个出现的值推断列类型；找不到就给 TStr。
+    -- \| 按第一个值推断类型
     inferType n = case [v | r <- rows, Just v <- [lookup n r]] of
         (VInt _ : _) -> TInt
         (VStr _ : _) -> TStr
         (VBool _ : _) -> TBool
         [] -> TStr
 
--- | 先 describe 拿列，再 scan 拿行；describe 拿不到时退回扫行推断。
+-- | 扫一张表拼成 Table
 loadTable :: String -> IO Table
 loadTable t = do
     schemaR <- doDescribeTable t
     case schemaR of
-        Right cols -> do
+        Right (cols, _n) -> do
             rowsR <- doScan t
             case rowsR of
                 Right rows -> pure (Table t (schemaToColumns cols) rows)
@@ -302,30 +351,41 @@ loadTable t = do
                 Right rows -> pure (Table t (inferColumns rows) rows)
                 Left _ -> pure (Table t [] [])
 
--- * MonadStorage 实例
 
--- | IPC 实现：所有方法都走管道。
+-- * MonadStorage 实例
+-- | 存储方法全走管道
 instance MonadStorage IPCStorage where
-    -- \| 发 Scan。
+    -- \| 发 Scan
     scan t = IPCStorage (doScan t)
 
-    -- \| 发 Insert，不带索引键。
+    -- \| 发 Insert
     insert t r = IPCStorage (doInsert t r)
 
-    -- \| 发 ReplaceAll。
+    -- \| 发 ReplaceAll
     replaceAll t rs = IPCStorage (doReplaceAll t rs)
 
-    -- \| 发 LookupByIndex。
+    -- \| 发 LookupByIndex
     lookupByKey t k = IPCStorage (doLookupByKey t k)
 
-    -- \| ListTables + 逐表 (describe, scan)，拼成 Database。
+    -- \| 发 CreateTable
+    createTable name cols = IPCStorage (doCreateTable name (map toWire cols))
+      where
+        -- \| 本地列类型转线上字符串
+        toWire (n, TInt) = SchemaColumn n "int"
+        toWire (n, TStr) = SchemaColumn n "str"
+        toWire (n, TBool) = SchemaColumn n "bool"
+
+    -- \| 发 DropTable
+    dropTable name = IPCStorage (doDropTable name)
+
+    -- \| 列表 + 逐表扫描拼库
     snapshot = IPCStorage $ do
         result <- doListTables
         case result of
             Left _ -> pure []
             Right ts -> mapM loadDbEntry ts
       where
-        -- \| 加载一个 (表名, 表) 对。
+        -- \| 加载一个 (表名, 表) 对
         loadDbEntry t = do
             tbl <- loadTable t
             pure (t, tbl)
diff --git a/chusql-engine/src/ChuSQL/Storage/Memory.hs b/chusql-engine/src/ChuSQL/Storage/Memory.hs
index 03e5332..0e9b46f 100644
--- a/chusql-engine/src/ChuSQL/Storage/Memory.hs
+++ b/chusql-engine/src/ChuSQL/Storage/Memory.hs
@@ -3,16 +3,19 @@ module ChuSQL.Storage.Memory (MemoryStorage (runMemoryStorage)) where
 import ChuSQL.Model
 import ChuSQL.Storage
 
--- | 内存实现：本质是 Database 上的 State，错误通道是 Either String。
+-- 内存实现：状态是 Database，错误通道是 Either String。
+
+-- * 实例
+-- | 内存存储：Database 上的状态
 newtype MemoryStorage a = MemoryStorage {runMemoryStorage :: Database -> Either String (a, Database)}
 
--- | Functor：把 fmap 转发给底下的 State。
+-- | Functor：转发给底层状态
 instance Functor MemoryStorage where
     fmap f (MemoryStorage m) = MemoryStorage $ \db -> do
         (a, db') <- m db
         Right (f a, db')
 
--- | Applicative：转发 pure / <*>。
+-- | Applicative：转发 pure 和 <*>
 instance Applicative MemoryStorage where
     pure x = MemoryStorage $ \db -> Right (x, db)
     MemoryStorage mf <*> MemoryStorage ma = MemoryStorage $ \db -> do
@@ -20,47 +23,60 @@ instance Applicative MemoryStorage where
         (a, db2) <- ma db1
         Right (f a, db2)
 
--- | Monad：顺序执行，把动作转发给底下的 State。
+-- | Monad：顺序执行
 instance Monad MemoryStorage where
     MemoryStorage m >>= k = MemoryStorage $ \db -> do
         (a, db') <- m db
         runMemoryStorage (k a) db'
 
--- | MonadStorage 实例：内存里直接改 Database。
+-- | MonadStorage：直接改内存库
 instance MonadStorage MemoryStorage where
-    -- \| 按名查表，返回所有行。
+    -- \| 全表扫描
     scan t = MemoryStorage $ \db -> do
         tbl <- lookupTable db t
         Right (Right (tableRows tbl), db)
 
-    -- \| 追加一行到表尾。
+    -- \| 追加一行
     insert t r = MemoryStorage $ \db -> do
         tbl <- lookupTable db t
         Right (Right (), replaceTable t tbl{tableRows = tableRows tbl ++ [r]} db)
 
-    -- \| 用新行列表替换整表内容。
+    -- \| 整表替换
     replaceAll t rows = MemoryStorage $ \db -> do
         tbl <- lookupTable db t
         Right (Right (), replaceTable t tbl{tableRows = rows} db)
 
-    -- \| 找 id 列等于 k 的第一行。
+    -- \| 按主键找第一行
     lookupByKey t k = MemoryStorage $ \db -> do
         tbl <- lookupTable db t
         Right (Right (findRow tbl k), db)
 
-    -- \| 原样返回当前数据库。
+    -- \| 建空表；已存在报错
+    createTable name cols = MemoryStorage $ \db ->
+        if any ((== name) . fst) db
+            then Right (Left ("table already exists: " ++ name), db)
+            else Right (Right (), db ++ [(name, Table name cols [])])
+
+    -- \| 删表；不存在报错
+    dropTable name = MemoryStorage $ \db ->
+        if any ((== name) . fst) db
+            then Right (Right (), filter ((/= name) . fst) db)
+            else Right (Left ("unknown table: " ++ name), db)
+
+    -- \| 原样返回当前库
     snapshot = MemoryStorage $ \db -> Right (db, db)
 
--- | 按 id 列匹配一个整数。
+-- * 工具
+-- | 按 id 列找一行
 findRow :: Table -> Int -> Maybe Row
 findRow tbl k = case filter matches (tableRows tbl) of
     (r : _) -> Just r
     [] -> Nothing
   where
-    -- \| 这行的 id 列是否等于 k。
+    -- \| 这行的 id 是否等于 k
     matches r = lookup "id" r == Just (VInt k)
 
--- | 用给定表替换同名表；不存在就原样返回。
+-- | 用给定表替换同名表
 replaceTable :: String -> Table -> Database -> Database
 replaceTable name table =
     map (\(n, t) -> if n == name then (n, table) else (n, t))
diff --git a/chusql-engine/src/ChuSQL/Syntax/AST.hs b/chusql-engine/src/ChuSQL/Syntax/AST.hs
index a4f57e6..7dff886 100644
--- a/chusql-engine/src/ChuSQL/Syntax/AST.hs
+++ b/chusql-engine/src/ChuSQL/Syntax/AST.hs
@@ -1,9 +1,12 @@
-module ChuSQL.Syntax.AST (Query (..), FromClause (..), Expr (..), SortDir (..), makeSelect) where
+module ChuSQL.Syntax.AST (Statement (..), FromClause (..), Expr (..), SortDir (..), makeSelect) where
 
--- SQL 语法树：四类语句（SELECT / INSERT / DELETE / UPDATE）+ 表达式、FROM 从句、排序方向。
+import ChuSQL.Model (Column (..))
 
--- 查询语句
-data Query
+-- 语法树：语句、数据来源、条件表达式、排序方向。
+
+-- * 语句
+-- | 一条语句：查 / 加 / 删 / 改 / 建表 / 删表
+data Statement
     = Select
         { selectCols :: [String]
         , selectFrom :: FromClause
@@ -14,15 +17,18 @@ data Query
     | Insert String [String] [Expr]
     | Delete String (Maybe Expr)
     | Update String [(String, Expr)] (Maybe Expr)
+    | CreateTable String [(String, Column)]
+    | DropTable String
     deriving (Show, Eq)
 
--- FROM 从句：单表或 JOIN。
+-- | 数据来源：单表，或两表拼接
 data FromClause
     = FromTable (Maybe String) String
     | FromJoin FromClause (Maybe String) String Expr
     deriving (Show, Eq)
 
--- 条件表达式
+-- * 表达式
+-- | 条件表达式
 data Expr
     = Col String
     | LitInt Int
@@ -35,14 +41,16 @@ data Expr
     | Or Expr Expr
     deriving (Show, Eq)
 
--- 排序方向
+-- * 排序
+-- | 排序方向
 data SortDir
     = Asc
     | Desc
     deriving (Show, Eq)
 
--- 便捷构造：造一条最简单的 SELECT（给测试和演示用）。
-makeSelect :: [String] -> String -> Maybe Expr -> Query
+-- * 构造
+-- | 造一个最简单的 SELECT
+makeSelect :: [String] -> String -> Maybe Expr -> Statement
 makeSelect cols tbl w =
     Select
         { selectCols = cols
diff --git a/chusql-engine/src/ChuSQL/Syntax/Parser.hs b/chusql-engine/src/ChuSQL/Syntax/Parser.hs
index 9b5cd77..4cbd4f5 100644
--- a/chusql-engine/src/ChuSQL/Syntax/Parser.hs
+++ b/chusql-engine/src/ChuSQL/Syntax/Parser.hs
@@ -1,7 +1,8 @@
 {-# LANGUAGE ImportQualifiedPost #-}
 
-module ChuSQL.Syntax.Parser (parseQuery) where
+module ChuSQL.Syntax.Parser (parseStatement) where
 
+import ChuSQL.Model (Column (..))
 import ChuSQL.Syntax.AST
 import Control.Monad.Combinators.Expr (Operator (..), makeExprParser)
 import Data.Char (isAlpha, isAlphaNum, toLower)
@@ -12,48 +13,50 @@ import Text.Megaparsec
 import Text.Megaparsec.Char
 import Text.Megaparsec.Char.Lexer qualified as Lxr
 
--- SQL 解析器：把 SQL 文本解析成 AST。词法层管空白、关键字、标识符、字面量与符号；
--- 语法层按优先级 比较 > AND > OR 自底向上组装表达式。
+-- SQL 解析：词法 + 语法，把文本变成语句树。
 
+-- * 词法
+-- | 解析器类型
 type Parser = Parsec Void String
 
--- * 词法层
 
--- | 跳过空白（含换行）。
+-- | 跳过空白
 sc :: Parser ()
 sc = Lxr.space space1 empty empty
 
--- | 消费一个词法单元以及其后的空白。
+-- | 词后面吃掉空白
 lexeme :: Parser a -> Parser a
 lexeme = Lxr.lexeme sc
 
--- | 匹配一个符号（如 ","、"("），并吃掉其后的空白。
+-- | 读一个符号
 symbol :: String -> Parser String
 symbol = Lxr.symbol sc
 
--- | 大小写不敏感的关键字；其后不能紧跟标识符字符，避免把 @selection@ 读成 @select@。
--- 整体用 'try' 包住：否则 @ORDER@ 会被 @keyword "or"@ 吃掉前缀 @OR@ 再报错，导致无法回溯。
+{- | 大小写不敏感的关键字；其后不能紧跟标识符字符，避免把 @selection@ 读成 @select@。
+整体用 'try' 包住：否则 @ORDER@ 会被 @keyword "or"@ 吃掉前缀 @OR@ 再报错，导致无法回溯。
+-}
+-- | 读关键字（不分大小写）
 keyword :: String -> Parser ()
 keyword k = lexeme $ try $ do
     _ <- string' k
     notFollowedBy (satisfy isIdentChar)
 
--- | 标识符：字母或下划线开头，其后可跟字母、数字或下划线。
+-- | 读一个名字
 identifier :: Parser String
 identifier = lexeme $ do
     first <- satisfy (\ch -> isAlpha ch || ch == '_')
     rest <- many (satisfy isIdentChar)
     return (first : rest)
 
--- | 标识符允许的字符：字母、数字或下划线。
+-- | 名字里允许的字符
 isIdentChar :: Char -> Bool
 isIdentChar ch = isAlphaNum ch || ch == '_'
 
--- | 十进制整数字面量。
+-- | 读一个整数
 integer :: Parser Int
 integer = lexeme Lxr.decimal
 
--- | 单引号字符串字面量，遵循标准 SQL 转义规则：
+-- | 读一个字符串字面量
 stringLit :: Parser String
 stringLit = lexeme $ do
     _ <- char '\''
@@ -61,8 +64,10 @@ stringLit = lexeme $ do
     _ <- char '\''
     return s
 
--- | 字符串内的一个字符：@''@ 折叠成一个单引号，其余字符（含反斜杠）原样保留。
--- 两个分支都不会在失败时消耗输入，因此可以安全地放进 'many'。
+{- | 字符串内的一个字符：@''@ 折叠成一个单引号，其余字符（含反斜杠）原样保留。
+两个分支都不会在失败时消耗输入，因此可以安全地放进 'many'。
+-}
+-- | 字符串里的一个字符
 stringChar :: Parser Char
 stringChar =
     choice
@@ -70,31 +75,34 @@ stringChar =
         , satisfy (/= '\'')
         ]
 
--- | 解析 ASC/DESC
+-- * 子句
+-- | 升序或降序
 sortDir :: Parser SortDir
 sortDir = (Desc <$ keyword "desc") <|> (Asc <$ keyword "asc") <|> pure Asc
 
--- | 解析 LIMIT
+-- | LIMIT 后面的整数
 limitClause :: Parser Int
 limitClause = do
     keyword "limit"
     integer
 
--- | 解析JOIN和限定列名
+-- | 能带表名的列名
 qualifiedName :: Parser String
 qualifiedName = do
     first <- identifier
     rest <- many (symbol "." *> identifier)
     return (intercalate "." (first : rest))
 
--- * 表达式层
 
--- | 表达式入口，最低优先级。
+-- * 表达式
+-- | 读一个表达式
 expr :: Parser Expr
 expr = makeExprParser atom operatorTable
 
--- | 运算符表。注意 'makeExprParser' 要求各层按优先级从高到低排列：
--- 比较运算符绑定最紧，'AND' 次之，'OR' 最松。
+{- | 运算符表。注意 'makeExprParser' 要求各层按优先级从高到低排列：
+比较运算符绑定最紧，'AND' 次之，'OR' 最松。
+-}
+-- | 运算符优先级（从紧到松）
 operatorTable :: [[Operator Parser Expr]]
 operatorTable =
     [
@@ -106,7 +114,7 @@ operatorTable =
     , [InfixL (Or <$ keyword "OR")] -- 最低优先级
     ]
 
--- | 原子表达式：字面量、列引用或括号表达式。
+-- | 最小的表达式单位
 atom :: Parser Expr
 atom =
     choice
@@ -116,23 +124,22 @@ atom =
         , between (symbol "(") (symbol ")") expr
         ]
 
--- * 语句层
 
--- | 显式指定排序的语句
+-- | 一个排序列
 orderItem :: Parser (String, SortDir)
 orderItem = do
     col <- qualifiedName
     dir <- sortDir
     return (col, dir)
 
--- | @ORDER BY col [ASC|DESC], ...@。
+-- | ORDER BY 的列表
 orderByClause :: Parser [(String, SortDir)]
 orderByClause = do
     keyword "order"
     keyword "by"
     sepBy1 orderItem (symbol ",")
 
--- | @col = expr@，用于 UPDATE 的 SET 子句。
+-- | SET 里的一条赋值
 assignment :: Parser (String, Expr)
 assignment = do
     col <- identifier
@@ -140,9 +147,8 @@ assignment = do
     e <- expr
     return (col, e)
 
--- * 从句层
 
--- | SQL 保留字，不能用作表别名
+-- | 保留字清单
 reservedWords :: [String]
 reservedWords =
     [ "select"
@@ -163,24 +169,28 @@ reservedWords =
     , "delete"
     , "update"
     , "set"
+    , "create"
+    , "table"
     ]
 
--- | 表别名。别名不能是保留字：否则 @FROM users WHERE age > 18@ 会把 @WHERE@
--- 当成 @users@ 的别名吃掉，后面真正的 WHERE 子句就再也解析不到。
--- 用 'try' 包住，一旦命中保留字就整体回溯，让 'optional' 正常返回 'Nothing'。
+{- | 表别名。别名不能是保留字：否则 @FROM users WHERE age > 18@ 会把 @WHERE@
+当成 @users@ 的别名吃掉，后面真正的 WHERE 子句就再也解析不到。
+用 'try' 包住，一旦命中保留字就整体回溯，让 'optional' 正常返回 'Nothing'。
+-}
+-- | 别名（不许用保留字）
 aliasName :: Parser String
 aliasName = try $ do
     name <- identifier
     if map toLower name `elem` reservedWords then empty else return name
 
--- | @表名 [别名]@。
+-- | 表名 + 可选别名
 tableRef :: Parser (Maybe String, String)
 tableRef = do
     tbl <- identifier
     mAlias <- optional aliasName
     return (mAlias, tbl)
 
--- | @JOIN 表 [别名] ON 条件@。
+-- | 一个 JOIN ... ON
 joinClause :: Parser (Maybe String, String, Expr)
 joinClause = do
     keyword "join"
@@ -189,14 +199,14 @@ joinClause = do
     cond <- expr
     return (mAlias, tbl, cond)
 
--- | FROM 从句：一张表 + 任意多个 JOIN。
+-- | FROM 子句（可含多个 JOIN）
 fromClause :: Parser FromClause
 fromClause = do
     (mAlias, tbl) <- tableRef
     joins <- many joinClause
     return (foldl (\acc (a, t, c) -> FromJoin acc a t c) (FromTable mAlias tbl) joins)
 
--- | 选择列表：@*@ 或逗号分隔的列名。
+-- | SELECT 的列清单
 selectList :: Parser [String]
 selectList =
     choice
@@ -204,9 +214,46 @@ selectList =
         , (:) <$> qualifiedName <*> many (symbol "," *> qualifiedName)
         ]
 
--- | @SELECT ... FROM ... [WHERE ...]@。
-selectQuery :: Parser Query
-selectQuery = do
+
+-- | 读 CREATE TABLE
+createTableStatement :: Parser Statement
+createTableStatement = do
+    keyword "create"
+    keyword "table"
+    name <- identifier
+    cols <- between (symbol "(") (symbol ")") (sepBy1 columnDef (symbol ","))
+    return (CreateTable name cols)
+
+-- | 读 DROP TABLE
+dropTableStatement :: Parser Statement
+dropTableStatement = do
+    keyword "drop"
+    keyword "table"
+    name <- identifier
+    return (DropTable name)
+
+-- | 建表时的一列
+columnDef :: Parser (String, Column)
+columnDef = do
+    name <- identifier
+    ty <- columnType
+    return (name, ty)
+
+-- | 列类型关键字
+columnType :: Parser Column
+columnType =
+    (keyword "integer" >> pure TInt)
+        <|> (keyword "int" >> pure TInt)
+        <|> (keyword "varchar" >> pure TStr)
+        <|> (keyword "text" >> pure TStr)
+        <|> (keyword "str" >> pure TStr)
+        <|> (keyword "boolean" >> pure TBool)
+        <|> (keyword "bool" >> pure TBool)
+
+-- * 语句
+-- | 读 SELECT
+selectStatement :: Parser Statement
+selectStatement = do
     keyword "select"
     cols <- selectList
     keyword "from"
@@ -223,9 +270,9 @@ selectQuery = do
             , selectLimit = mLimit
             }
 
--- | @INSERT ... INTO ... VALUES ...@。
-insertQuery :: Parser Query
-insertQuery = do
+-- | 读 INSERT
+insertStatement :: Parser Statement
+insertStatement = do
     keyword "INSERT"
     keyword "INTO"
     tbl <- identifier
@@ -242,18 +289,18 @@ insertQuery = do
             (sepBy1 atom (symbol ","))
     return (Insert tbl cols vals)
 
--- | @DELETE ... FROM ... [WHERE ...]@。
-deleteQuery :: Parser Query
-deleteQuery = do
+-- | 读 DELETE
+deleteStatement :: Parser Statement
+deleteStatement = do
     keyword "DELETE"
     keyword "FROM"
     tbl <- identifier
     mWhere <- optional (keyword "WHERE" *> expr)
     return (Delete tbl mWhere)
 
--- | UPDATE ... SET col = val, ... [WHERE ...]@
-updateQuery :: Parser Query
-updateQuery = do
+-- | 读 UPDATE
+updateStatement :: Parser Statement
+updateStatement = do
     keyword "update"
     tbl <- identifier
     keyword "set"
@@ -261,9 +308,19 @@ updateQuery = do
     mWhere <- optional (keyword "where" *> expr)
     return (Update tbl assigns mWhere)
 
--- | 解析一条完整的语句；失败时返回可直接展示的错误信息。
-parseQuery :: String -> Either String Query
-parseQuery input =
-    case runParser (sc *> (selectQuery <|> insertQuery <|> deleteQuery <|> updateQuery) <* sc <* eof) "<query>" input of
+-- * 入口
+-- | 解析总入口
+parseStatement :: String -> Either String Statement
+parseStatement input =
+    case runParser (sc *> statementP <* sc <* eof) "<query>" input of
         Left err -> Left (errorBundlePretty err)
         Right q -> Right q
+  where
+    -- \| 依次尝试各种语句
+    statementP =
+        selectStatement
+            <|> insertStatement
+            <|> deleteStatement
+            <|> updateStatement
+            <|> createTableStatement
+            <|> dropTableStatement
diff --git a/chusql-engine/test/Spec.hs b/chusql-engine/test/Spec.hs
index 06a3415..f377aea 100644
--- a/chusql-engine/test/Spec.hs
+++ b/chusql-engine/test/Spec.hs
@@ -62,19 +62,19 @@ main = hspec $ do
 
     describe "ChuSQL.Syntax.Parser" $ do
         it "parses a simple SELECT" $ do
-            parseQuery "SELECT name FROM users"
+            parseStatement "SELECT name FROM users"
                 `shouldBe` Right (makeSelect ["name"] "users" Nothing)
 
         it "parses SELECT *" $ do
-            parseQuery "SELECT * FROM users"
+            parseStatement "SELECT * FROM users"
                 `shouldBe` Right (makeSelect ["*"] "users" Nothing)
 
         it "parses multiple columns" $ do
-            parseQuery "SELECT name, age FROM users"
+            parseStatement "SELECT name, age FROM users"
                 `shouldBe` Right (makeSelect ["name", "age"] "users" Nothing)
 
         it "parses WHERE with >" $ do
-            parseQuery "SELECT name FROM users WHERE age > 18"
+            parseStatement "SELECT name FROM users WHERE age > 18"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -83,7 +83,7 @@ main = hspec $ do
                     )
 
         it "parses AND" $ do
-            parseQuery "SELECT name FROM users WHERE age > 18 AND age < 30"
+            parseStatement "SELECT name FROM users WHERE age > 18 AND age < 30"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -97,7 +97,7 @@ main = hspec $ do
                     )
 
         it "parses OR" $ do
-            parseQuery "SELECT name FROM users WHERE age < 18 OR age > 60"
+            parseStatement "SELECT name FROM users WHERE age < 18 OR age > 60"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -111,7 +111,7 @@ main = hspec $ do
                     )
 
         it "is case-insensitive for keywords" $ do
-            parseQuery "select name from users where age > 18"
+            parseStatement "select name from users where age > 18"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -120,11 +120,11 @@ main = hspec $ do
                     )
 
         it "tolerates extra whitespace" $ do
-            parseQuery "SELECT   name   FROM   users"
+            parseStatement "SELECT   name   FROM   users"
                 `shouldBe` Right (makeSelect ["name"] "users" Nothing)
 
         it "parses a string literal in WHERE" $ do
-            parseQuery "SELECT name FROM users WHERE name = 'Alice'"
+            parseStatement "SELECT name FROM users WHERE name = 'Alice'"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -133,7 +133,7 @@ main = hspec $ do
                     )
 
         it "uses standard SQL escaping: '' is one quote" $ do
-            parseQuery "SELECT name FROM users WHERE name = 'It''s ok'"
+            parseStatement "SELECT name FROM users WHERE name = 'It''s ok'"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -142,7 +142,7 @@ main = hspec $ do
                     )
 
         it "treats a backslash as an ordinary character" $ do
-            parseQuery "SELECT name FROM users WHERE name = 'a\\b'"
+            parseStatement "SELECT name FROM users WHERE name = 'a\\b'"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -151,7 +151,7 @@ main = hspec $ do
                     )
 
         it "parses an empty string literal" $ do
-            parseQuery "SELECT name FROM users WHERE name = ''"
+            parseStatement "SELECT name FROM users WHERE name = ''"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -160,7 +160,7 @@ main = hspec $ do
                     )
 
         it "parses a string that is a single quote" $ do
-            parseQuery "SELECT name FROM users WHERE name = ''''"
+            parseStatement "SELECT name FROM users WHERE name = ''''"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -169,15 +169,15 @@ main = hspec $ do
                     )
 
         it "rejects an unterminated string literal" $ do
-            parseQuery "SELECT name FROM users WHERE name = 'oops"
+            parseStatement "SELECT name FROM users WHERE name = 'oops"
                 `shouldSatisfy` isLeft
 
         it "allows digits inside identifiers" $ do
-            parseQuery "SELECT user1 FROM users"
+            parseStatement "SELECT user1 FROM users"
                 `shouldBe` Right (makeSelect ["user1"] "users" Nothing)
 
         it "honours parentheses and AND/OR precedence" $ do
-            parseQuery "SELECT name FROM users WHERE (age > 18 OR age < 5) AND name = 'Bob'"
+            parseStatement "SELECT name FROM users WHERE (age > 18 OR age < 5) AND name = 'Bob'"
                 `shouldBe` Right
                     ( makeSelect
                         ["name"]
@@ -194,16 +194,16 @@ main = hspec $ do
                     )
 
         it "rejects trailing junk after a complete query" $ do
-            parseQuery "SELECT name FROM users extra junk"
+            parseStatement "SELECT name FROM users extra junk"
                 `shouldSatisfy` isLeft
 
         it "returns Left on missing table name" $ do
-            parseQuery "SELECT name FROM"
+            parseStatement "SELECT name FROM"
                 `shouldSatisfy` isLeft
 
     describe "ChuSQL.Syntax.Parser (JOIN)" $ do
         it "parses a simple JOIN without aliases" $ do
-            parseQuery "SELECT name FROM users JOIN orders ON id = user_id"
+            parseStatement "SELECT name FROM users JOIN orders ON id = user_id"
                 `shouldBe` Right
                     ( Select
                         { selectCols = ["name"]
@@ -220,7 +220,7 @@ main = hspec $ do
                     )
 
         it "parses JOIN with aliases" $ do
-            parseQuery "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id"
+            parseStatement "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id"
                 `shouldBe` Right
                     ( Select
                         { selectCols = ["u.name"]
@@ -237,13 +237,13 @@ main = hspec $ do
                     )
 
         it "parses qualified column names" $ do
-            case parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id" of
+            case parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id" of
                 Right q -> selectCols q `shouldBe` ["u.name", "o.product"]
                 Left err -> expectationFailure err
 
     describe "ChuSQL.Engine (SELECT)" $ do
         it "returns all rows without WHERE" $ do
-            rowsOf (runQuery testDB (makeSelect ["*"] "users" Nothing))
+            rowsOf (runStatement testDB (makeSelect ["*"] "users" Nothing))
                 `shouldBe` Right
                     [ [("id", VInt 1), ("name", VStr "Alice"), ("age", VInt 25)]
                     , [("id", VInt 2), ("name", VStr "Bob"), ("age", VInt 17)]
@@ -252,7 +252,7 @@ main = hspec $ do
 
         it "filters with WHERE" $ do
             rowsOf
-                ( runQuery
+                ( runStatement
                     testDB
                     ( makeSelect
                         ["name"]
@@ -266,7 +266,7 @@ main = hspec $ do
                     ]
 
         it "projects only the requested columns" $ do
-            rowsOf (runQuery testDB (makeSelect ["name"] "users" Nothing))
+            rowsOf (runStatement testDB (makeSelect ["name"] "users" Nothing))
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Bob")]
@@ -274,11 +274,11 @@ main = hspec $ do
                     ]
 
         it "returns Left for an unknown table" $ do
-            runQuery testDB (makeSelect ["name"] "nonexistent" Nothing)
+            runStatement testDB (makeSelect ["name"] "nonexistent" Nothing)
                 `shouldSatisfy` isLeft
 
         it "returns Left for an unknown column" $ do
-            runQuery
+            runStatement
                 testDB
                 ( makeSelect
                     ["name"]
@@ -288,31 +288,31 @@ main = hspec $ do
                 `shouldSatisfy` isLeft
 
         it "returns Left when WHERE is not a boolean" $ do
-            runQuery testDB (makeSelect ["name"] "users" (Just (Col "age")))
+            runStatement testDB (makeSelect ["name"] "users" (Just (Col "age")))
                 `shouldSatisfy` isLeft
 
         it "returns Left for an unknown projected column" $ do
-            runQuery testDB (makeSelect ["nope"] "users" Nothing)
+            runStatement testDB (makeSelect ["nope"] "users" Nothing)
                 `shouldSatisfy` isLeft
 
     describe "ChuSQL.Engine (INSERT)" $ do
         it "parses a simple INSERT" $ do
-            parseQuery "INSERT INTO users (name, age) VALUES ('Dave', 22)"
+            parseStatement "INSERT INTO users (name, age) VALUES ('Dave', 22)"
                 `shouldBe` Right (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22])
 
         it "parses INSERT with a single column" $ do
-            parseQuery "INSERT INTO users (name) VALUES ('Eve')"
+            parseStatement "INSERT INTO users (name) VALUES ('Eve')"
                 `shouldBe` Right (Insert "users" ["name"] [LitStr "Eve"])
 
         it "parses INSERT case-insensitively" $ do
-            parseQuery "insert into users (name, age) values ('Dave', 22)"
+            parseStatement "insert into users (name, age) values ('Dave', 22)"
                 `shouldBe` Right (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22])
 
         it "executes INSERT and adds a row at the end" $ do
-            case runQuery testDB (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22]) of
+            case runStatement testDB (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22]) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name", "age"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name", "age"] "users" Nothing))
                         `shouldBe` Right
                             [ [("name", VStr "Alice"), ("age", VInt 25)]
                             , [("name", VStr "Bob"), ("age", VInt 17)]
@@ -321,76 +321,76 @@ main = hspec $ do
                             ]
 
         it "does not modify the original database" $ do
-            case runQuery testDB (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22]) of
+            case runStatement testDB (Insert "users" ["name", "age"] [LitStr "Dave", LitInt 22]) of
                 Left err -> expectationFailure err
                 Right (_, _) -> do
-                    rowsOf (runQuery testDB (makeSelect ["name"] "users" Nothing))
+                    rowsOf (runStatement testDB (makeSelect ["name"] "users" Nothing))
                         `shouldSatisfy` \r -> case r of
                             Right rows -> length rows == 3
                             Left _ -> False
 
         it "returns Left when column count does not match value count" $ do
-            runQuery testDB (Insert "users" ["name", "age"] [LitStr "Dave"])
+            runStatement testDB (Insert "users" ["name", "age"] [LitStr "Dave"])
                 `shouldSatisfy` isLeft
 
         it "returns Left for an unknown table" $ do
-            runQuery testDB (Insert "nonexistent" ["name"] [LitStr "X"])
+            runStatement testDB (Insert "nonexistent" ["name"] [LitStr "X"])
                 `shouldSatisfy` isLeft
 
         it "returns Left when a value has the wrong type for comparison" $ do
-            runQuery testDB (Insert "users" ["name"] [Col "other"])
+            runStatement testDB (Insert "users" ["name"] [Col "other"])
                 `shouldSatisfy` isLeft
 
     describe "ChuSQL.Engine (DELETE)" $ do
         it "parses DELETE with WHERE" $ do
-            parseQuery "DELETE FROM users WHERE age < 18"
+            parseStatement "DELETE FROM users WHERE age < 18"
                 `shouldBe` Right (Delete "users" (Just (Lt (Col "age") (LitInt 18))))
 
         it "parses DELETE without WHERE" $ do
-            parseQuery "DELETE FROM users"
+            parseStatement "DELETE FROM users"
                 `shouldBe` Right (Delete "users" Nothing)
 
         it "parses DELETE case-insensitively" $ do
-            parseQuery "delete from users where age < 18"
+            parseStatement "delete from users where age < 18"
                 `shouldBe` Right (Delete "users" (Just (Lt (Col "age") (LitInt 18))))
 
         it "executes DELETE with WHERE, removing matching rows" $ do
-            case runQuery testDB (Delete "users" (Just (Lt (Col "age") (LitInt 18)))) of
+            case runStatement testDB (Delete "users" (Just (Lt (Col "age") (LitInt 18)))) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name"] "users" Nothing))
                         `shouldBe` Right
                             [ [("name", VStr "Alice")]
                             , [("name", VStr "Carol")]
                             ]
 
         it "executes DELETE without WHERE, removing all rows" $ do
-            case runQuery testDB (Delete "users" Nothing) of
+            case runStatement testDB (Delete "users" Nothing) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name"] "users" Nothing))
                         `shouldBe` Right []
 
         it "does not modify the original database" $ do
-            case runQuery testDB (Delete "users" Nothing) of
+            case runStatement testDB (Delete "users" Nothing) of
                 Left err -> expectationFailure err
                 Right (_, _) -> do
-                    rowsOf (runQuery testDB (makeSelect ["name"] "users" Nothing))
+                    rowsOf (runStatement testDB (makeSelect ["name"] "users" Nothing))
                         `shouldSatisfy` \r -> case r of
                             Right rows -> length rows == 3
                             Left _ -> False
 
         it "returns Left for an unknown table" $ do
-            runQuery testDB (Delete "nonexistent" Nothing)
+            runStatement testDB (Delete "nonexistent" Nothing)
                 `shouldSatisfy` isLeft
 
         it "returns Left when WHERE references an unknown column" $ do
-            runQuery testDB (Delete "users" (Just (Gt (Col "unknown") (LitInt 18))))
+            runStatement testDB (Delete "users" (Just (Gt (Col "unknown") (LitInt 18))))
                 `shouldSatisfy` isLeft
 
     describe "ChuSQL.Engine (UPDATE)" $ do
         it "parses UPDATE with WHERE" $ do
-            parseQuery "UPDATE users SET age = 26 WHERE name = 'Alice'"
+            parseStatement "UPDATE users SET age = 26 WHERE name = 'Alice'"
                 `shouldBe` Right
                     ( Update
                         "users"
@@ -399,12 +399,12 @@ main = hspec $ do
                     )
 
         it "parses UPDATE without WHERE" $ do
-            parseQuery "UPDATE users SET age = 26"
+            parseStatement "UPDATE users SET age = 26"
                 `shouldBe` Right
                     (Update "users" [("age", LitInt 26)] Nothing)
 
         it "parses multiple assignments" $ do
-            parseQuery "UPDATE users SET age = 26, name = 'Dave'"
+            parseStatement "UPDATE users SET age = 26, name = 'Dave'"
                 `shouldBe` Right
                     ( Update
                         "users"
@@ -413,7 +413,7 @@ main = hspec $ do
                     )
 
         it "parses UPDATE case-insensitively" $ do
-            parseQuery "update users set age = 26 where name = 'Alice'"
+            parseStatement "update users set age = 26 where name = 'Alice'"
                 `shouldBe` Right
                     ( Update
                         "users"
@@ -422,10 +422,10 @@ main = hspec $ do
                     )
 
         it "executes UPDATE with WHERE, modifying matching rows" $ do
-            case runQuery testDB (Update "users" [("age", LitInt 99)] (Just (Eq (Col "name") (LitStr "Alice")))) of
+            case runStatement testDB (Update "users" [("age", LitInt 99)] (Just (Eq (Col "name") (LitStr "Alice")))) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name", "age"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name", "age"] "users" Nothing))
                         `shouldBe` Right
                             [ [("name", VStr "Alice"), ("age", VInt 99)]
                             , [("name", VStr "Bob"), ("age", VInt 17)]
@@ -433,10 +433,10 @@ main = hspec $ do
                             ]
 
         it "executes UPDATE without WHERE, modifying all rows" $ do
-            case runQuery testDB (Update "users" [("age", LitInt 0)] Nothing) of
+            case runStatement testDB (Update "users" [("age", LitInt 0)] Nothing) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name", "age"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name", "age"] "users" Nothing))
                         `shouldBe` Right
                             [ [("name", VStr "Alice"), ("age", VInt 0)]
                             , [("name", VStr "Bob"), ("age", VInt 0)]
@@ -444,10 +444,10 @@ main = hspec $ do
                             ]
 
         it "applies multiple assignments to each row" $ do
-            case runQuery testDB (Update "users" [("age", LitInt 99), ("name", LitStr "X")] Nothing) of
+            case runStatement testDB (Update "users" [("age", LitInt 99), ("name", LitStr "X")] Nothing) of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (runQuery db' (makeSelect ["name", "age"] "users" Nothing))
+                    rowsOf (runStatement db' (makeSelect ["name", "age"] "users" Nothing))
                         `shouldBe` Right
                             [ [("name", VStr "X"), ("age", VInt 99)]
                             , [("name", VStr "X"), ("age", VInt 99)]
@@ -455,51 +455,51 @@ main = hspec $ do
                             ]
 
         it "does not modify the original database" $ do
-            case runQuery testDB (Update "users" [("age", LitInt 0)] Nothing) of
+            case runStatement testDB (Update "users" [("age", LitInt 0)] Nothing) of
                 Left err -> expectationFailure err
                 Right (_, _) -> do
-                    rowsOf (runQuery testDB (makeSelect ["name"] "users" Nothing))
+                    rowsOf (runStatement testDB (makeSelect ["name"] "users" Nothing))
                         `shouldSatisfy` \r -> case r of
                             Right rows -> length rows == 3
                             Left _ -> False
 
         it "returns Left for an unknown table" $ do
-            runQuery testDB (Update "nonexistent" [("age", LitInt 0)] Nothing)
+            runStatement testDB (Update "nonexistent" [("age", LitInt 0)] Nothing)
                 `shouldSatisfy` isLeft
 
         it "returns Left when WHERE references an unknown column" $ do
-            runQuery testDB (Update "users" [("age", LitInt 0)] (Just (Gt (Col "unknown") (LitInt 1))))
+            runStatement testDB (Update "users" [("age", LitInt 0)] (Just (Gt (Col "unknown") (LitInt 1))))
                 `shouldSatisfy` isLeft
 
         it "returns Left when SET references an unknown column" $ do
-            runQuery testDB (Update "users" [("unknown", LitInt 0)] Nothing)
+            runStatement testDB (Update "users" [("unknown", LitInt 0)] Nothing)
                 `shouldSatisfy` \r -> case r of
                     Right _ -> True
                     Left _ -> True
 
     describe "ChuSQL.Engine (ORDER BY)" $ do
         it "parses ORDER BY ASC" $ do
-            case parseQuery "SELECT name FROM users ORDER BY age ASC" of
+            case parseStatement "SELECT name FROM users ORDER BY age ASC" of
                 Right q -> selectOrderBy q `shouldBe` [("age", Asc)]
                 Left err -> expectationFailure err
 
         it "parses ORDER BY DESC" $ do
-            case parseQuery "SELECT name FROM users ORDER BY age DESC" of
+            case parseStatement "SELECT name FROM users ORDER BY age DESC" of
                 Right q -> selectOrderBy q `shouldBe` [("age", Desc)]
                 Left err -> expectationFailure err
 
         it "defaults to ASC" $ do
-            case parseQuery "SELECT name FROM users ORDER BY age" of
+            case parseStatement "SELECT name FROM users ORDER BY age" of
                 Right q -> selectOrderBy q `shouldBe` [("age", Asc)]
                 Left err -> expectationFailure err
 
         it "parses multiple ORDER BY columns" $ do
-            case parseQuery "SELECT name FROM users ORDER BY age DESC, name ASC" of
+            case parseStatement "SELECT name FROM users ORDER BY age DESC, name ASC" of
                 Right q -> selectOrderBy q `shouldBe` [("age", Desc), ("name", Asc)]
                 Left err -> expectationFailure err
 
         it "parses without ORDER BY" $ do
-            case parseQuery "SELECT name FROM users" of
+            case parseStatement "SELECT name FROM users" of
                 Right q -> selectOrderBy q `shouldBe` []
                 Left err -> expectationFailure err
 
@@ -512,7 +512,7 @@ main = hspec $ do
                         , selectOrderBy = [("age", Asc)]
                         , selectLimit = Nothing
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Bob")]
                     , [("name", VStr "Alice")]
@@ -528,7 +528,7 @@ main = hspec $ do
                         , selectOrderBy = [("age", Desc)]
                         , selectLimit = Nothing
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Carol")]
                     , [("name", VStr "Alice")]
@@ -544,7 +544,7 @@ main = hspec $ do
                         , selectOrderBy = [("name", Asc)]
                         , selectLimit = Nothing
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Bob")]
@@ -560,23 +560,23 @@ main = hspec $ do
                         , selectOrderBy = [("nope", Asc)]
                         , selectLimit = Nothing
                         }
-            runQuery testDB q `shouldSatisfy` isLeft
+            runStatement testDB q `shouldSatisfy` isLeft
 
     describe "ChuSQL.Engine (LIMIT)" $ do
         it "parses LIMIT" $ do
-            case parseQuery "SELECT * FROM users LIMIT 2" of
+            case parseStatement "SELECT * FROM users LIMIT 2" of
                 Right q -> selectLimit q `shouldBe` Just 2
                 Left err -> expectationFailure err
 
         it "parses LIMIT after ORDER BY" $ do
-            case parseQuery "SELECT * FROM users ORDER BY age DESC LIMIT 1" of
+            case parseStatement "SELECT * FROM users ORDER BY age DESC LIMIT 1" of
                 Right q -> do
                     selectOrderBy q `shouldBe` [("age", Desc)]
                     selectLimit q `shouldBe` Just 1
                 Left err -> expectationFailure err
 
         it "parses without LIMIT" $ do
-            case parseQuery "SELECT * FROM users" of
+            case parseStatement "SELECT * FROM users" of
                 Right q -> selectLimit q `shouldBe` Nothing
                 Left err -> expectationFailure err
 
@@ -589,7 +589,7 @@ main = hspec $ do
                         , selectOrderBy = []
                         , selectLimit = Just 2
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Bob")]
@@ -604,7 +604,7 @@ main = hspec $ do
                         , selectOrderBy = [("age", Desc)]
                         , selectLimit = Just 2
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Carol")]
                     , [("name", VStr "Alice")]
@@ -619,7 +619,7 @@ main = hspec $ do
                         , selectOrderBy = []
                         , selectLimit = Just 10
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Bob")]
@@ -635,16 +635,16 @@ main = hspec $ do
                         , selectOrderBy = []
                         , selectLimit = Just 0
                         }
-            rowsOf (runQuery testDB q)
+            rowsOf (runStatement testDB q)
                 `shouldBe` Right []
 
         it "rejects negative LIMIT" $ do
-            parseQuery "SELECT * FROM users LIMIT -1"
+            parseStatement "SELECT * FROM users LIMIT -1"
                 `shouldSatisfy` isLeft
 
     describe "ChuSQL.Engine (JOIN)" $ do
         it "executes a two-table JOIN with aliases" $ do
-            rowsOf (parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("u.name", VStr "Alice"), ("o.product", VStr "Book")]
                     , [("u.name", VStr "Alice"), ("o.product", VStr "Cup")]
@@ -652,14 +652,14 @@ main = hspec $ do
                     ]
 
         it "executes JOIN with WHERE" $ do
-            rowsOf (parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("u.name", VStr "Alice"), ("o.product", VStr "Book")]
                     , [("u.name", VStr "Alice"), ("o.product", VStr "Cup")]
                     ]
 
         it "executes JOIN with ORDER BY" $ do
-            rowsOf (parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id ORDER BY o.product DESC" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id ORDER BY o.product DESC" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("u.name", VStr "Bob"), ("o.product", VStr "Pen")]
                     , [("u.name", VStr "Alice"), ("o.product", VStr "Cup")]
@@ -667,14 +667,14 @@ main = hspec $ do
                     ]
 
         it "executes JOIN with LIMIT" $ do
-            rowsOf (parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id LIMIT 2" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id LIMIT 2" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("u.name", VStr "Alice"), ("o.product", VStr "Book")]
                     , [("u.name", VStr "Alice"), ("o.product", VStr "Cup")]
                     ]
 
         it "returns Left when JOIN table not found" $ do
-            runQuery
+            runStatement
                 testDB
                 ( Select
                     { selectCols = ["u.name"]
@@ -692,7 +692,7 @@ main = hspec $ do
                 `shouldSatisfy` isLeft
 
         it "returns Left when ON references an unknown column" $ do
-            runQuery
+            runStatement
                 testDB
                 ( Select
                     { selectCols = ["u.name"]
@@ -711,7 +711,7 @@ main = hspec $ do
 
     describe "ChuSQL end-to-end" $ do
         it "parses and executes a simple query" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE age > 18" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE age > 18" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Carol")]
@@ -719,8 +719,8 @@ main = hspec $ do
 
         it "parses and executes a complex query" $ do
             rowsOf
-                ( parseQuery "SELECT name FROM users WHERE age < 18 OR age > 28"
-                    >>= runQuery testDB
+                ( parseStatement "SELECT name FROM users WHERE age < 18 OR age > 28"
+                    >>= runStatement testDB
                 )
                 `shouldBe` Right
                     [ [("name", VStr "Bob")]
@@ -728,14 +728,14 @@ main = hspec $ do
                     ]
 
         it "returns Left when parsing fails" $ do
-            (parseQuery "SELECT name FROM" >>= runQuery testDB)
+            (parseStatement "SELECT name FROM" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "INSERT then SELECT end-to-end" $ do
-            case parseQuery "INSERT INTO users (name, age) VALUES ('Dave', 22)" >>= runQuery testDB of
+            case parseStatement "INSERT INTO users (name, age) VALUES ('Dave', 22)" >>= runStatement testDB of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (parseQuery "SELECT name FROM users WHERE age > 18" >>= runQuery db')
+                    rowsOf (parseStatement "SELECT name FROM users WHERE age > 18" >>= runStatement db')
                         `shouldBe` Right
                             [ [("name", VStr "Alice")]
                             , [("name", VStr "Carol")]
@@ -743,19 +743,19 @@ main = hspec $ do
                             ]
 
         it "DELETE then SELECT end-to-end" $ do
-            case parseQuery "DELETE FROM users WHERE age > 20" >>= runQuery testDB of
+            case parseStatement "DELETE FROM users WHERE age > 20" >>= runStatement testDB of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (parseQuery "SELECT name FROM users" >>= runQuery db')
+                    rowsOf (parseStatement "SELECT name FROM users" >>= runStatement db')
                         `shouldBe` Right
                             [ [("name", VStr "Bob")]
                             ]
 
         it "UPDATE then SELECT end-to-end" $ do
-            case parseQuery "UPDATE users SET age = 99 WHERE name = 'Alice'" >>= runQuery testDB of
+            case parseStatement "UPDATE users SET age = 99 WHERE name = 'Alice'" >>= runStatement testDB of
                 Left err -> expectationFailure err
                 Right (db', _) -> do
-                    rowsOf (parseQuery "SELECT name, age FROM users" >>= runQuery db')
+                    rowsOf (parseStatement "SELECT name, age FROM users" >>= runStatement db')
                         `shouldBe` Right
                             [ [("name", VStr "Alice"), ("age", VInt 99)]
                             , [("name", VStr "Bob"), ("age", VInt 17)]
@@ -763,27 +763,27 @@ main = hspec $ do
                             ]
 
         it "ORDER BY with WHERE end-to-end" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE age > 18 ORDER BY age DESC" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE age > 18 ORDER BY age DESC" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Carol")]
                     , [("name", VStr "Alice")]
                     ]
 
         it "ORDER BY with LIMIT end-to-end" $ do
-            rowsOf (parseQuery "SELECT name FROM users ORDER BY age DESC LIMIT 2" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users ORDER BY age DESC LIMIT 2" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Carol")]
                     , [("name", VStr "Alice")]
                     ]
 
         it "WHERE ORDER BY LIMIT end-to-end" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE age > 15 ORDER BY age DESC LIMIT 1" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE age > 15 ORDER BY age DESC LIMIT 1" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Carol")]
                     ]
 
         it "JOIN with WHERE and ORDER BY end-to-end" $ do
-            rowsOf (parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 15 ORDER BY o.product" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 15 ORDER BY o.product" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("u.name", VStr "Alice"), ("o.product", VStr "Book")]
                     , [("u.name", VStr "Alice"), ("o.product", VStr "Cup")]
@@ -804,7 +804,7 @@ main = hspec $ do
             sameResultAsUnoptimized "SELECT * FROM users"
 
         it "pushes a single-side predicate into the left side of a JOIN" $ do
-            case parseQuery "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" of
+            case parseStatement "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" of
                 Left err -> expectationFailure err
                 Right q ->
                     case translate q of
@@ -813,7 +813,7 @@ main = hspec $ do
                             filterPushedIntoLeft (optimize testDB relOp) `shouldBe` True
 
         it "removes a redundant SELECT * projection" $ do
-            case parseQuery "SELECT * FROM users" of
+            case parseStatement "SELECT * FROM users" of
                 Left err -> expectationFailure err
                 Right q ->
                     case translate q of
@@ -827,7 +827,7 @@ main = hspec $ do
             optimize testDB relOp `shouldBe` relOp
 
         it "is idempotent after reaching a fixed point" $ do
-            case parseQuery "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" of
+            case parseStatement "SELECT u.name, o.product FROM users u JOIN orders o ON u.id = o.user_id WHERE u.age > 20" of
                 Left err -> expectationFailure err
                 Right q ->
                     case translate q of
@@ -872,11 +872,11 @@ main = hspec $ do
             sameResultAsUnoptimized "SELECT name FROM users WHERE 'abc' > 1"
 
         it "returns no rows for a constant-false predicate" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE 1 > 2" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE 1 > 2" >>= runStatement testDB)
                 `shouldBe` Right []
 
         it "returns every row for a constant-true predicate" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE 1 = 1" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE 1 = 1" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Bob")]
@@ -961,123 +961,123 @@ main = hspec $ do
 
     describe "ChuSQL.Semantic" $ do
         it "rejects an unknown column in WHERE" $ do
-            (parseQuery "SELECT name FROM users WHERE nope > 18" >>= runQuery testDB)
+            (parseStatement "SELECT name FROM users WHERE nope > 18" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in WHERE even when the table is empty" $ do
-            (parseQuery "SELECT name FROM users WHERE nope > 18" >>= runQuery emptyDB)
+            (parseStatement "SELECT name FROM users WHERE nope > 18" >>= runStatement emptyDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in an ON condition" $ do
-            (parseQuery "SELECT u.name FROM users u JOIN orders o ON u.nope = o.user_id" >>= runQuery testDB)
+            (parseStatement "SELECT u.name FROM users u JOIN orders o ON u.nope = o.user_id" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a type mismatch inside a comparison" $ do
-            (parseQuery "SELECT name FROM users WHERE name > 18" >>= runQuery testDB)
+            (parseStatement "SELECT name FROM users WHERE name > 18" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a type mismatch even when the table is empty" $ do
-            (parseQuery "SELECT name FROM users WHERE name > 18" >>= runQuery emptyDB)
+            (parseStatement "SELECT name FROM users WHERE name > 18" >>= runStatement emptyDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a WHERE clause that is not a condition" $ do
-            (parseQuery "SELECT name FROM users WHERE age" >>= runQuery testDB)
+            (parseStatement "SELECT name FROM users WHERE age" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a non-boolean WHERE even when the table is empty" $ do
-            (parseQuery "SELECT name FROM users WHERE age" >>= runQuery emptyDB)
+            (parseStatement "SELECT name FROM users WHERE age" >>= runStatement emptyDB)
                 `shouldSatisfy` isLeft
 
         it "rejects comparing two different types with =" $ do
-            (parseQuery "SELECT name FROM users WHERE name = 18" >>= runQuery testDB)
+            (parseStatement "SELECT name FROM users WHERE name = 18" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in INSERT" $ do
-            (parseQuery "INSERT INTO users (nickname) VALUES (1)" >>= runQuery testDB)
+            (parseStatement "INSERT INTO users (nickname) VALUES (1)" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a value whose type does not match the column" $ do
-            (parseQuery "INSERT INTO users (name, age) VALUES ('Dave', 'abc')" >>= runQuery testDB)
+            (parseStatement "INSERT INTO users (name, age) VALUES ('Dave', 'abc')" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in UPDATE SET" $ do
-            (parseQuery "UPDATE users SET nope = 1" >>= runQuery testDB)
+            (parseStatement "UPDATE users SET nope = 1" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in DELETE WHERE" $ do
-            (parseQuery "DELETE FROM users WHERE nope > 1" >>= runQuery testDB)
+            (parseStatement "DELETE FROM users WHERE nope > 1" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "still accepts a valid query" $ do
-            rowsOf (parseQuery "SELECT name FROM users WHERE age > 18" >>= runQuery testDB)
+            rowsOf (parseStatement "SELECT name FROM users WHERE age > 18" >>= runStatement testDB)
                 `shouldBe` Right
                     [ [("name", VStr "Alice")]
                     , [("name", VStr "Carol")]
                     ]
 
         it "rejects an UPDATE whose value has the wrong type" $ do
-            (parseQuery "UPDATE users SET age = 'abc'" >>= runQuery testDB)
+            (parseStatement "UPDATE users SET age = 'abc'" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects a type mismatch in an ON condition" $ do
-            (parseQuery "SELECT u.name FROM users u JOIN orders o ON u.name = o.user_id" >>= runQuery testDB)
+            (parseStatement "SELECT u.name FROM users u JOIN orders o ON u.name = o.user_id" >>= runStatement testDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in DELETE WHERE even when the table is empty" $ do
-            (parseQuery "DELETE FROM users WHERE nope > 1" >>= runQuery emptyDB)
+            (parseStatement "DELETE FROM users WHERE nope > 1" >>= runStatement emptyDB)
                 `shouldSatisfy` isLeft
 
         it "rejects an unknown column in UPDATE SET even when the table is empty" $ do
-            (parseQuery "UPDATE users SET nope = 1" >>= runQuery emptyDB)
+            (parseStatement "UPDATE users SET nope = 1" >>= runStatement emptyDB)
                 `shouldSatisfy` isLeft
 
         it "currently allows an INSERT that leaves a column out (known gap)" $ do
-            (parseQuery "INSERT INTO users (name) VALUES ('Eve')" >>= runQuery testDB)
+            (parseStatement "INSERT INTO users (name) VALUES ('Eve')" >>= runStatement testDB)
                 `shouldSatisfy` isRight
 
         it "says which clause is wrong and which columns are available" $ do
-            case parseQuery "SELECT name FROM users WHERE nope > 18" >>= runQuery testDB of
+            case parseStatement "SELECT name FROM users WHERE nope > 18" >>= runStatement testDB of
                 Right _ -> expectationFailure "expected a Left"
                 Left err -> do
                     err `shouldContain` "unknown column in WHERE"
                     err `shouldContain` "available: id, name, age"
 
         it "names INSERT when a target column does not exist" $ do
-            case parseQuery "INSERT INTO users (nickname) VALUES (1)" >>= runQuery testDB of
+            case parseStatement "INSERT INTO users (nickname) VALUES (1)" >>= runStatement testDB of
                 Right _ -> expectationFailure "expected a Left"
                 Left err -> err `shouldContain` "unknown column in INSERT"
 
         it "names ORDER BY when a sort key does not exist" $ do
-            case parseQuery "SELECT name FROM users ORDER BY nope" >>= runQuery testDB of
+            case parseStatement "SELECT name FROM users ORDER BY nope" >>= runStatement testDB of
                 Right _ -> expectationFailure "expected a Left"
                 Left err -> err `shouldContain` "unknown column in ORDER BY"
 
         it "names ON and both types when a join condition mismatches" $ do
-            case parseQuery "SELECT u.name FROM users u JOIN orders o ON u.name = o.user_id" >>= runQuery testDB of
+            case parseStatement "SELECT u.name FROM users u JOIN orders o ON u.name = o.user_id" >>= runStatement testDB of
                 Right _ -> expectationFailure "expected a Left"
                 Left err -> do
                     err `shouldContain` "ON: both sides of ="
                     err `shouldContain` "TStr and TInt"
 
         it "names the column and the expected type when an assignment has the wrong type" $ do
-            case parseQuery "UPDATE users SET age = 'abc'" >>= runQuery testDB of
+            case parseStatement "UPDATE users SET age = 'abc'" >>= runStatement testDB of
                 Right _ -> expectationFailure "expected a Left"
                 Left err -> err `shouldContain` "UPDATE: column age needs TInt, got TStr"
 
         it "accepts SELECT * across a join (the sentinel is not a column)" $ do
-            (parseQuery "SELECT * FROM users u JOIN orders o ON u.id = o.user_id" >>= runQuery testDB)
+            (parseStatement "SELECT * FROM users u JOIN orders o ON u.id = o.user_id" >>= runStatement testDB)
                 `shouldSatisfy` isRight
 
     describe "ChuSQL.Algebra.Op" $ do
         it "renders a plan as indented text" $ do
-            case parseQuery "SELECT name FROM users WHERE age > 18" >>= translate of
+            case parseStatement "SELECT name FROM users WHERE age > 18" >>= translate of
                 Left err -> expectationFailure err
                 Right plan ->
                     renderPlan plan
                         `shouldBe` "Project [\"name\"]\n  Filter Gt (Col \"age\") (LitInt 18)\n    Scan Nothing \"users\""
 
         it "renders a join plan with indentation" $ do
-            case parseQuery "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id" >>= translate of
+            case parseStatement "SELECT u.name FROM users u JOIN orders o ON u.id = o.user_id" >>= translate of
                 Left err -> expectationFailure err
                 Right plan ->
                     lines (renderPlan plan)
@@ -1088,7 +1088,7 @@ main = hspec $ do
                                    ]
 
         it "renders a sort and limit plan" $ do
-            case parseQuery "SELECT name FROM users ORDER BY age DESC LIMIT 2" >>= translate of
+            case parseStatement "SELECT name FROM users ORDER BY age DESC LIMIT 2" >>= translate of
                 Left err -> expectationFailure err
                 Right plan ->
                     lines (renderPlan plan)
@@ -1180,7 +1180,67 @@ main = hspec $ do
             withPipeName "chusql-no-such-server" $ do
                 result <- runIPCStorage (scan "users")
                 result `shouldSatisfy` isLeft
+        it "parses CREATE TABLE with two columns" $ do
+            parseStatement "CREATE TABLE users (id INT, name TEXT)"
+                `shouldBe` Right (CreateTable "users" [("id", TInt), ("name", TStr)])
 
+        it "parses CREATE TABLE case-insensitively" $ do
+            parseStatement "create table users (id int, name text)"
+                `shouldBe` Right (CreateTable "users" [("id", TInt), ("name", TStr)])
+
+        it "parses CREATE TABLE with BOOL column" $ do
+            parseStatement "CREATE TABLE t (flag BOOL)"
+                `shouldBe` Right (CreateTable "t" [("flag", TBool)])
+
+        it "parses CREATE TABLE with VARCHAR as TStr" $ do
+            parseStatement "CREATE TABLE t (name VARCHAR)"
+                `shouldBe` Right (CreateTable "t" [("name", TStr)])
+
+        it "parses CREATE TABLE with INTEGER" $ do
+            parseStatement "CREATE TABLE t (id INTEGER)"
+                `shouldBe` Right (CreateTable "t" [("id", TInt)])
+
+        it "rejects CREATE TABLE without columns" $ do
+            parseStatement "CREATE TABLE t ()"
+                `shouldSatisfy` isLeft
+
+        it "rejects CREATE TABLE with missing type" $ do
+            parseStatement "CREATE TABLE t (id)"
+                `shouldSatisfy` isLeft
+
+    describe "ChuSQL.Engine (CREATE TABLE)" $ do
+        it "creates a table in memory" $ do
+            case runStatement testDB (CreateTable "newt" [("id", TInt), ("name", TStr)]) of
+                Left err -> expectationFailure err
+                Right (db', _) -> do
+                    rowsOf (runStatement db' (makeSelect ["*"] "newt" Nothing))
+                        `shouldBe` Right []
+
+        it "rejects creating an existing table" $ do
+            runStatement testDB (CreateTable "users" [("id", TInt)])
+                `shouldSatisfy` isLeft
+
+        it "rejects duplicate column names" $ do
+            runStatement testDB (CreateTable "dup" [("id", TInt), ("id", TStr)])
+                `shouldSatisfy` isLeft
+
+        it "rejects empty column list at parse time" $ do
+            parseStatement "CREATE TABLE t ()"
+                `shouldSatisfy` isLeft
+        it "parses DROP TABLE" $ do
+            parseStatement "DROP TABLE users"
+                `shouldBe` Right (DropTable "users")
+
+        it "drops a table in memory" $ do
+            case runStatement testDB (DropTable "users") of
+                Left e -> expectationFailure e
+                Right (db', _) -> do
+                    runStatement db' (makeSelect ["*"] "users" Nothing)
+                        `shouldSatisfy` isLeft
+
+        it "rejects dropping a nonexistent table" $ do
+            runStatement testDB (DropTable "nope")
+                `shouldSatisfy` isLeft
 emptyDB :: Database
 emptyDB = [(n, t{tableRows = []}) | (n, t) <- testDB]
 
@@ -1305,7 +1365,7 @@ isRight (Left _) = False
 
 sameResultAsUnoptimized :: String -> Expectation
 sameResultAsUnoptimized sql =
-    case parseQuery sql of
+    case parseStatement sql of
         Left err -> expectationFailure err
         Right q ->
             case translate q of
@@ -1319,7 +1379,7 @@ filterPushedIntoLeft _ = False
 
 optimizedPlan :: String -> Either String RelOp
 optimizedPlan sql = do
-    q <- parseQuery sql
+    q <- parseStatement sql
     optimize testDB <$> translate q
 
 firstFilterCond :: RelOp -> Maybe Expr
@@ -1353,7 +1413,7 @@ stripProjects (Lookup t k) = Lookup t k
 
 projectedPlan :: String -> Either String RelOp
 projectedPlan sql = do
-    q <- parseQuery sql
+    q <- parseStatement sql
     plan <- translate q
     Right (pushProject testDB ["*"] plan)
 
diff --git a/chusql-storage/src/bin/server.rs b/chusql-storage/src/bin/server.rs
index ab78164..a4387b9 100644
--- a/chusql-storage/src/bin/server.rs
+++ b/chusql-storage/src/bin/server.rs
@@ -1,17 +1,15 @@
-//! 命名管道服务：按行读写 JSON。Windows 上管道名映射为 \\.\pipe\<name>。
-//! 启动时读配置（环境变量 → TOML → 默认值）并把每项来源打进日志。
 
-use std::collections::BTreeSet;
+use std::collections::{BTreeSet, HashMap};
 use std::io::{BufRead, BufReader, Write};
 use std::path::PathBuf;
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 use std::thread;
 
 use chusql_storage::catalog::Catalog;
 use chusql_storage::config::{self, Config, Loaded};
 use chusql_storage::heap::HeapTable;
 use chusql_storage::log;
-use chusql_storage::protocol::{Request, Response};
+use chusql_storage::protocol::{Request, Response, SchemaColumn};
 use chusql_storage::wal::{Wal, WalOp};
 use chusql_storage::{log_debug, log_error, log_info, log_warn};
 use interprocess::local_socket::{
@@ -21,308 +19,413 @@ use interprocess::local_socket::{
 };
 use interprocess::TryClone;
 
-// * 路径
+// 命名管道服务：按行读写 JSON，Windows 上映射成 \\.\pipe\<name>。
+// 启动时读配置并把每项来源打进日志；表句柄按名字缓存复用。
 
-/// 表名 -> 数据文件路径。
-fn table_path(cfg: &Config, table: &str) -> PathBuf {
-    cfg.data_dir.join(format!("{}.db", table))
+// 服务器
+/// 服务器状态：配置 + 表句柄缓存 + 写锁
+struct Server {
+    cfg: Config,
+    tables: Mutex<HashMap<String, Arc<Mutex<HeapTable>>>>,
+    write_lock: Mutex<()>,
 }
 
-/// 表名 -> 索引文件路径。
-fn index_path(cfg: &Config, table: &str) -> PathBuf {
-    cfg.data_dir.join(format!("{}.idx", table))
-}
+impl Server {
+    /// 新建服务器状态
+    fn new(cfg: Config) -> std::io::Result<Self> {
+        std::fs::create_dir_all(&cfg.data_dir)?;
+        Ok(Server {
+            cfg,
+            tables: Mutex::new(HashMap::new()),
+            write_lock: Mutex::new(()),
+        })
+    }
 
-/// 数据字典文件路径。
-fn catalog_path(cfg: &Config) -> PathBuf {
-    cfg.data_dir.join("catalog.json")
-}
 
-/// WAL 文件路径。
-fn wal_path(cfg: &Config) -> PathBuf {
-    cfg.data_dir.join("wal.log")
-}
+// 路径
+    /// 表名 -> 数据文件
+    fn table_path(&self, table: &str) -> PathBuf {
+        self.cfg.data_dir.join(format!("{}.db", table))
+    }
 
-// * 表操作
+    /// 表名 -> 索引文件
+    fn index_path(&self, table: &str) -> PathBuf {
+        self.cfg.data_dir.join(format!("{}.idx", table))
+    }
 
-/// 打开一张表，执行闭包；表不存在就创建。
-fn with_table<R>(
-    cfg: &Config,
-    table: &str,
-    f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
-) -> std::io::Result<R> {
-    std::fs::create_dir_all(&cfg.data_dir)?;
-    let mut t = HeapTable::open(table_path(cfg, table), cfg.page_size)?;
-    f(&mut t)
-}
+    /// 数据字典文件
+    fn catalog_path(&self) -> PathBuf {
+        self.cfg.data_dir.join("catalog.json")
+    }
 
-/// 打开带索引的表，执行闭包。
-fn with_indexed_table<R>(
-    cfg: &Config,
-    table: &str,
-    f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
-) -> std::io::Result<R> {
-    std::fs::create_dir_all(&cfg.data_dir)?;
-    let mut t = HeapTable::open_indexed(
-        table_path(cfg, table),
-        index_path(cfg, table),
-        cfg.page_size,
-        cfg.btree_order,
-    )?;
-    f(&mut t)
-}
+    /// WAL 文件
+    fn wal_path(&self) -> PathBuf {
+        self.cfg.data_dir.join("wal.log")
+    }
 
-/// 表文件是否存在且非空。
-fn table_exists(cfg: &Config, table: &str) -> bool {
-    let p = table_path(cfg, table);
-    std::fs::metadata(&p).map(|m| m.len() > 0).unwrap_or(false)
-}
 
-/// 打开已存在的表；不存在返回 NotFound。
-fn with_existing_table<R>(
-    cfg: &Config,
-    table: &str,
-    f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
-) -> std::io::Result<R> {
-    if !table_exists(cfg, table) {
-        return Err(std::io::Error::new(
+// 表句柄
+    /// 表文件存在且非空
+    fn table_exists(&self, table: &str) -> bool {
+        if self.tables.lock().unwrap().contains_key(table) {
+            return true;
+        }
+        if let Ok(c) = Catalog::load(self.catalog_path()) {
+            if c.describe(table).is_some() {
+                return true;
+            }
+        }
+        std::fs::metadata(self.table_path(table))
+            .map(|m| m.len() > 0)
+            .unwrap_or(false)
+    }
+
+    /// 拿表句柄（缓存复用）
+    fn table_handle(&self, table: &str) -> std::io::Result<Arc<Mutex<HeapTable>>> {
+        let mut map = self.tables.lock().unwrap();
+        if let Some(h) = map.get(table) {
+            return Ok(h.clone());
+        }
+        std::fs::create_dir_all(&self.cfg.data_dir)?;
+        let t = HeapTable::open_indexed(
+            self.table_path(table),
+            self.index_path(table),
+            self.cfg.page_size,
+            self.cfg.btree_order,
+            self.cfg.pool_size,
+        )?;
+        let h = Arc::new(Mutex::new(t));
+        map.insert(table.to_string(), h.clone());
+        Ok(h)
+    }
+
+    /// 在表上跑闭包
+    fn with_table<R>(
+        &self,
+        table: &str,
+        f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
+    ) -> std::io::Result<R> {
+        let h = self.table_handle(table)?;
+        let mut guard = h.lock().unwrap();
+        f(&mut guard)
+    }
+
+    /// 同上，但一定带索引
+    fn with_indexed_table<R>(
+        &self,
+        table: &str,
+        f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
+    ) -> std::io::Result<R> {
+        self.with_table(table, f)
+    }
+
+    /// 表不存在就报错
+    fn with_existing_table<R>(
+        &self,
+        table: &str,
+        f: impl FnOnce(&mut HeapTable) -> std::io::Result<R>,
+    ) -> std::io::Result<R> {
+        if !self.table_exists(table) {
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::NotFound,
+                format!("unknown table: {}", table),
+            ));
+        }
+        self.with_table(table, f)
+    }
+
+// 写入路径
+    /// 把一条 WAL 操作落到磁盘
+    fn apply_op(&self, op: &WalOp) -> std::io::Result<()> {
+        match op {
+            WalOp::Insert { table, row, key } => {
+                match key {
+                    None => self.with_table(table, |t| t.insert(row))?,
+                    Some(k) => self.with_indexed_table(table, |t| t.insert_keyed(row, *k))?,
+                }
+                let mut c = Catalog::load(self.catalog_path())?;
+                let row: chusql_storage::protocol::Row = row.clone().into_iter().collect();
+                c.record_insert(table, &row);
+                c.save(self.catalog_path())?;
+                Ok(())
+            }
+            WalOp::ReplaceAll { table, rows } => {
+                self.with_indexed_table(table, |t| t.replace_all(rows))?;
+                let mut c = Catalog::load(self.catalog_path())?;
+                let rows: Vec<chusql_storage::protocol::Row> =
+                    rows.iter().map(|r| r.clone().into_iter().collect()).collect();
+                c.record_replace_all(table, &rows);
+                c.save(self.catalog_path())?;
+                Ok(())
+            }
+        }
+    }
+
+    /// 先写 WAL 再改数据
+    fn write_via_wal(&self, op: &WalOp) -> std::io::Result<()> {
+        let _guard = self.write_lock.lock().unwrap();
+        std::fs::create_dir_all(&self.cfg.data_dir)?;
+        let wal = Wal::new(self.wal_path());
+
+        wal.clear()?;
+
+        wal.append(op)?;
+
+        let result = self.apply_op(op);
+
+        if result.is_ok() {
+            if let Err(e) = self.flush_op_tables(op) {
+                return Err(e);
+            }
+        }
+
+        wal.clear()?;
+        result
+    }
+
+    /// 把涉及的表写回磁盘
+    fn flush_op_tables(&self, op: &WalOp) -> std::io::Result<()> {
+        match op {
+            WalOp::Insert { table, key, .. } => {
+                if key.is_some() {
+                    self.with_indexed_table(table, |t| t.flush())
+                } else {
+                    self.with_table(table, |t| t.flush())
+                }
+            }
+            WalOp::ReplaceAll { table, .. } => {
+                self.with_indexed_table(table, |t| t.flush())
+            }
+        }
+    }
+
+    /// 启动时重放残留 WAL
+    fn recover_wal(&self) -> std::io::Result<()> {
+        std::fs::create_dir_all(&self.cfg.data_dir)?;
+        let wal = Wal::new(self.wal_path());
+        match wal.read()? {
+            None => Ok(()),
+            Some(op) => {
+                log_warn!(core, "replaying incomplete WAL entry");
+                self.apply_op(&op)?;
+                wal.clear()?;
+                log_info!(core, "WAL replay complete");
+                Ok(())
+            }
+        }
+    }
+
+
+// 请求分发
+    /// 一条请求翻成一条响应
+    fn handle_request(&self, req: Request) -> Response {
+        match req {
+            Request::Ping => {
+                log_debug!(pipe, "ping");
+                Response::Pong
+            }
+
+            Request::Scan { table } => {
+                log_debug!(pipe, "scan table={}", table);
+
+                let result = self.with_existing_table(&table, |t| t.scan());
+
+                match result {
+                    Ok(rows) => Response::Rows { rows },
+                    Err(e) => {
+                        log_warn!(pipe, "scan {}: {}", table, e);
+                        Response::Error {
+                            message: format!("scan {}: {}", table, e),
+                        }
+                    }
+                }
+            }
+
+            Request::Insert { table, row, key } => {
+                log_debug!(pipe, "insert table={} key={:?}", table, key);
+                let tname = table.clone();
+                let op = WalOp::Insert { table, row, key };
+                match self.write_via_wal(&op) {
+                    Ok(()) => Response::Ok,
+                    Err(e) => {
+                        log_warn!(pipe, "insert {}: {}", tname, e);
+                        Response::Error {
+                            message: format!("insert {}: {}", tname, e),
+                        }
+                    }
+                }
+            }
+
+            Request::LookupByIndex { table, key } => {
+                log_debug!(pipe, "lookup_by_index table={} key={}", table, key);
+                match self.with_indexed_table(&table, |t| t.get_by_key(key)) {
+                    Ok(Some(row)) => Response::Rows { rows: vec![row] },
+                    Ok(None) => Response::Rows { rows: vec![] },
+                    Err(e) => {
+                        log_warn!(pipe, "lookup_by_index {}: {}", table, e);
+                        Response::Error {
+                            message: format!("lookup_by_index {}: {}", table, e),
+                        }
+                    }
+                }
+            }
+
+            Request::ReplaceAll { table, rows } => {
+                log_debug!(pipe, "replace_all table={} rows={}", table, rows.len());
+                let tname = table.clone();
+                let op = WalOp::ReplaceAll { table, rows };
+                match self.write_via_wal(&op) {
+                    Ok(()) => Response::Ok,
+                    Err(e) => {
+                        log_warn!(pipe, "replace_all {}: {}", tname, e);
+                        Response::Error {
+                            message: format!("replace_all {}: {}", tname, e),
+                        }
+                    }
+                }
+            }
+
+            Request::ListTables => {
+                log_debug!(pipe, "list_tables");
+                match self.list_tables() {
+                    Ok(tables) => Response::Tables { tables },
+                    Err(e) => {
+                        log_warn!(pipe, "list_tables: {}", e);
+                        Response::Error {
+                            message: format!("list_tables: {}", e),
+                        }
+                    }
+                }
+            }
+
+            Request::DescribeTable { table } => {
+                log_debug!(pipe, "describe_table table={}", table);
+                match self.describe_table(&table) {
+                    Ok((cols, count)) => Response::Schema {
+                        columns: cols,
+                        row_count: count,
+                    },
+                    Err(e) => {
+                        log_warn!(pipe, "describe_table {}: {}", table, e);
+                        Response::Error {
+                            message: format!("describe_table {}: {}", table, e),
+                        }
+                    }
+                }
+            }
+
+            Request::CreateTable { table, columns } => {
+                log_debug!(pipe, "create_table table={} cols={}", table, columns.len());
+
+                let mut c = match Catalog::load(self.catalog_path()) {
+                    Ok(c) => c,
+                    Err(e) => {
+                        return Response::Error {
+                            message: format!("create_table {}: catalog: {}", table, e),
+                        }
+                    }
+                };
+                if c.describe(&table).is_some() {
+                    return Response::Error {
+                        message: format!("create_table {}: table already exists", table),
+                    };
+                }
+
+                if let Err(e) = self.with_table(&table, |_t| Ok(())) {
+                    return Response::Error {
+                        message: format!("create_table {}: {}", table, e),
+                    };
+                }
+
+                if let Err(e) = c.create_table(&table, columns) {
+                    return Response::Error {
+                        message: format!("create_table {}: {}", table, e),
+                    };
+                }
+                if let Err(e) = c.save(self.catalog_path()) {
+                    return Response::Error {
+                        message: format!("create_table {}: catalog save: {}", table, e),
+                    };
+                }
+
+                Response::Ok
+            }
+            Request::DropTable { table } => {
+                log_debug!(pipe, "drop_table table={}", table);
+
+                let mut c = match Catalog::load(self.catalog_path()) {
+                    Ok(c) => c,
+                    Err(e) => return Response::Error {
+                        message: format!("drop_table {}: catalog: {}", table, e),
+                    },
+                };
+                if let Err(e) = c.drop_table(&table) {
+                    return Response::Error {
+                        message: format!("drop_table {}: {}", table, e),
+                    };
+                }
+                if let Err(e) = c.save(self.catalog_path()) {
+                    return Response::Error {
+                        message: format!("drop_table {}: catalog save: {}", table, e),
+                    };
+                }
+
+                self.tables.lock().unwrap().remove(&table);
+
+                let _ = std::fs::remove_file(self.table_path(&table));
+                let _ = std::fs::remove_file(self.index_path(&table));
+
+                Response::Ok
+            }
+        }
+    }
+
+// 信息查询
+    /// 表名：catalog 与目录取并集
+    fn list_tables(&self) -> std::io::Result<Vec<String>> {
+        let mut names = BTreeSet::new();
+
+        let c = Catalog::load(self.catalog_path())?;
+        for t in c.table_names() {
+            names.insert(t);
+        }
+
+        let dir = &self.cfg.data_dir;
+        if dir.exists() {
+            for entry in std::fs::read_dir(dir)? {
+                let entry = entry?;
+                let name = entry.file_name().to_string_lossy().to_string();
+                if let Some(stem) = name.strip_suffix(".db") {
+                    names.insert(stem.to_string());
+                }
+            }
+        }
+
+        Ok(names.into_iter().collect())
+    }
+
+    /// 查一张表的 schema
+    fn describe_table(&self, table: &str) -> std::io::Result<(Vec<SchemaColumn>, u64)> {
+        let c = Catalog::load(self.catalog_path())?;
+        if let Some(schema) = c.describe(table) {
+            return Ok((schema.columns.clone(), schema.row_count));
+        }
+        if self.tables.lock().unwrap().contains_key(table)
+            || std::fs::metadata(self.table_path(table)).is_ok()
+        {
+            return Ok((Vec::new(), 0));
+        }
+        Err(std::io::Error::new(
             std::io::ErrorKind::NotFound,
             format!("unknown table: {}", table),
-        ));
-    }
-    let mut t = HeapTable::open(table_path(cfg, table), cfg.page_size)?;
-    f(&mut t)
-}
-
-// * 数据字典操作
-
-/// 读 catalog，按一行数据补列，再写回。
-fn catalog_add_row(
-    cfg: &Config,
-    table: &str,
-    row: &serde_json::Map<String, serde_json::Value>,
-) -> std::io::Result<()> {
-    let mut c = Catalog::load(catalog_path(cfg))?;
-    let row: chusql_storage::protocol::Row = row.clone().into_iter().collect();
-    c.ensure_columns(table, &row);
-    c.save(catalog_path(cfg))
-}
-
-/// 读 catalog，按多行数据补列，再写回。
-fn catalog_add_rows(
-    cfg: &Config,
-    table: &str,
-    rows: &[serde_json::Map<String, serde_json::Value>],
-) -> std::io::Result<()> {
-    let mut c = Catalog::load(catalog_path(cfg))?;
-    for r in rows {
-        let row: chusql_storage::protocol::Row = r.clone().into_iter().collect();
-        c.ensure_columns(table, &row);
-    }
-    c.save(catalog_path(cfg))
-}
-
-// * WAL 写路径与恢复
-
-/// 把一条 WAL 操作真正落到磁盘（堆表 + 索引 + catalog）。
-fn apply_op(cfg: &Config, op: &WalOp) -> std::io::Result<()> {
-    match op {
-        WalOp::Insert { table, row, key } => {
-            match key {
-                None => with_table(cfg, table, |t| t.insert(row))?,
-                Some(k) => with_indexed_table(cfg, table, |t| t.insert_keyed(row, *k))?,
-            }
-            let map: serde_json::Map<_, _> = row.clone().into_iter().collect();
-            catalog_add_row(cfg, table, &map)?;
-            Ok(())
-        }
-        WalOp::ReplaceAll { table, rows } => {
-            with_indexed_table(cfg, table, |t| t.replace_all(rows))?;
-            let maps: Vec<_> = rows.iter().map(|r| r.clone().into_iter().collect()).collect();
-            catalog_add_rows(cfg, table, &maps)?;
-            Ok(())
-        }
+        ))
     }
 }
 
-/// 写前日志 + 写数据 + 清空 WAL。
-///
-/// 顺序：clear（清掉上次已完成的） → append+fsync → apply → clear。
-/// 若中途进程被杀，重启时 WAL 里能读到那条操作并重放。
-fn write_via_wal(cfg: &Config, op: &WalOp) -> std::io::Result<()> {
-    let wal = Wal::new(wal_path(cfg));
 
-    // 清掉上一次遗留（正常情况下已经是空的）
-    wal.clear()?;
-
-    // 先写 WAL 并 fsync
-    wal.append(op)?;
-
-    // 再写数据
-    let result = apply_op(cfg, op);
-
-    // 无论 apply 成功还是返回 Err，都清空 WAL：
-    // 失败的操作不应被重放；若中途被杀，这里跑不到，WAL 会留到重启时重放。
-    wal.clear()?;
-
-    result
-}
-
-/// 启动时重放 WAL 里的残留操作。
-fn recover_wal(cfg: &Config) -> std::io::Result<()> {
-    let wal = Wal::new(wal_path(cfg));
-    match wal.read()? {
-        None => Ok(()),
-        Some(op) => {
-            log_warn!(core, "replaying incomplete WAL entry");
-            apply_op(cfg, &op)?;
-            wal.clear()?;
-            log_info!(core, "WAL replay complete");
-            Ok(())
-        }
-    }
-}
-
-// * 请求分发
-
-/// 把一条请求翻译成一条响应。
-fn handle_request(cfg: &Config, req: Request) -> Response {
-    match req {
-        Request::Ping => {
-            log_debug!(pipe, "ping");
-            Response::Pong
-        }
-
-        Request::Scan { table } => {
-            log_debug!(pipe, "scan table={}", table);
-            match with_existing_table(cfg, &table, |t| t.scan()) {
-                Ok(rows) => Response::Rows { rows },
-                Err(e) => {
-                    log_warn!(pipe, "scan {}: {}", table, e);
-                    Response::Error {
-                        message: format!("scan {}: {}", table, e),
-                    }
-                }
-            }
-        }
-
-        Request::Insert { table, row, key } => {
-            log_debug!(pipe, "insert table={} key={:?}", table, key);
-            let tname = table.clone();
-            let op = WalOp::Insert { table, row, key };
-            match write_via_wal(cfg, &op) {
-                Ok(()) => Response::Ok,
-                Err(e) => {
-                    log_warn!(pipe, "insert {}: {}", tname, e);
-                    Response::Error {
-                        message: format!("insert {}: {}", tname, e),
-                    }
-                }
-            }
-        }
-
-        Request::LookupByIndex { table, key } => {
-            log_debug!(pipe, "lookup_by_index table={} key={}", table, key);
-            match with_indexed_table(cfg, &table, |t| t.get_by_key(key)) {
-                Ok(Some(row)) => Response::Rows { rows: vec![row] },
-                Ok(None) => Response::Rows { rows: vec![] },
-                Err(e) => {
-                    log_warn!(pipe, "lookup_by_index {}: {}", table, e);
-                    Response::Error {
-                        message: format!("lookup_by_index {}: {}", table, e),
-                    }
-                }
-            }
-        }
-
-        Request::ReplaceAll { table, rows } => {
-            log_debug!(pipe, "replace_all table={} rows={}", table, rows.len());
-            let tname = table.clone();
-            let op = WalOp::ReplaceAll { table, rows };
-            match write_via_wal(cfg, &op) {
-                Ok(()) => Response::Ok,
-                Err(e) => {
-                    log_warn!(pipe, "replace_all {}: {}", tname, e);
-                    Response::Error {
-                        message: format!("replace_all {}: {}", tname, e),
-                    }
-                }
-            }
-        }
-
-        Request::ListTables => {
-            log_debug!(pipe, "list_tables");
-            match list_tables(cfg) {
-                Ok(tables) => Response::Tables { tables },
-                Err(e) => {
-                    log_warn!(pipe, "list_tables: {}", e);
-                    Response::Error {
-                        message: format!("list_tables: {}", e),
-                    }
-                }
-            }
-        }
-
-        Request::DescribeTable { table } => {
-            log_debug!(pipe, "describe_table table={}", table);
-            match describe_table(cfg, &table) {
-                Ok(cols) => Response::Schema { columns: cols },
-                Err(e) => {
-                    log_warn!(pipe, "describe_table {}: {}", table, e);
-                    Response::Error {
-                        message: format!("describe_table {}: {}", table, e),
-                    }
-                }
-            }
-        }
-    }
-}
-
-/// 列出表名：catalog 记录 + data 目录下的 .db 文件，取并集。
-fn list_tables(cfg: &Config) -> std::io::Result<Vec<String>> {
-    let mut names = BTreeSet::new();
-
-    let c = Catalog::load(catalog_path(cfg))?;
-    for t in c.table_names() {
-        names.insert(t);
-    }
-
-    let dir = &cfg.data_dir;
-    if dir.exists() {
-        for entry in std::fs::read_dir(dir)? {
-            let entry = entry?;
-            let name = entry.file_name().to_string_lossy().to_string();
-            if let Some(stem) = name.strip_suffix(".db") {
-                names.insert(stem.to_string());
-            }
-        }
-    }
-
-    Ok(names.into_iter().collect())
-}
-
-/// 查一张表的 schema。表在 catalog 里没有，但文件存在，返回空列。
-fn describe_table(
-    cfg: &Config,
-    table: &str,
-) -> std::io::Result<Vec<chusql_storage::protocol::SchemaColumn>> {
-    let c = Catalog::load(catalog_path(cfg))?;
-    if let Some(schema) = c.describe(table) {
-        return Ok(schema.columns.clone());
-    }
-    if table_exists(cfg, table) {
-        return Ok(Vec::new());
-    }
-    Err(std::io::Error::new(
-        std::io::ErrorKind::NotFound,
-        format!("unknown table: {}", table),
-    ))
-}
-
-// * 连接处理
-
-/// 处理一条连接：逐行读 JSON 请求，逐行回 JSON 响应。
-fn handle(cfg: &Config, conn: LocalSocketStream) -> std::io::Result<()> {
+// 连接
+/// 处理一条连接
+fn handle(server: &Server, conn: LocalSocketStream) -> std::io::Result<()> {
     let mut writer = conn.try_clone()?;
     let reader = BufReader::new(conn);
 
@@ -333,7 +436,7 @@ fn handle(cfg: &Config, conn: LocalSocketStream) -> std::io::Result<()> {
         }
 
         let resp = match serde_json::from_str::<Request>(&line) {
-            Ok(req) => handle_request(cfg, req),
+            Ok(req) => server.handle_request(req),
             Err(e) => {
                 log_warn!(pipe, "bad request line: {}", e);
                 Response::Error {
@@ -349,19 +452,20 @@ fn handle(cfg: &Config, conn: LocalSocketStream) -> std::io::Result<()> {
     Ok(())
 }
 
-// * 主入口
 
-/// 把"配置从哪来"打进日志。
+// 入口
+/// 把配置来源打进日志
 fn log_config(loaded: &Loaded) {
     match &loaded.config_path {
         Some(p) => log_info!(core, "config file: {}", p.display()),
         None => log_info!(core, "config file: none"),
     }
     for (name, value, origin) in &loaded.origins {
-        log_info!(core, "  {:<17} {} [{}]", name, value, origin.describe());
+        log_info!(core, "  {:<18} {} [{}]", name, value, origin.describe());
     }
 }
 
+/// 进程入口
 fn main() -> std::io::Result<()> {
     let loaded = match config::load() {
         Ok(l) => l,
@@ -376,15 +480,15 @@ fn main() -> std::io::Result<()> {
     log_info!(core, "chusql-storage {} starting", env!("CARGO_PKG_VERSION"));
     log_config(&loaded);
 
-    let cfg = Arc::new(loaded.config);
+    let server = Arc::new(Server::new(loaded.config)?);
 
-    // 启动时先重放 WAL，再做其他事
-    if let Err(e) = recover_wal(&cfg) {
+    if let Err(e) = server.recover_wal() {
         log_error!(core, "WAL recovery failed: {}", e);
         return Err(e);
     }
 
-    let ns_name = cfg
+    let ns_name = server
+        .cfg
         .pipe_name
         .as_str()
         .to_ns_name::<GenericNamespaced>()
@@ -394,16 +498,16 @@ fn main() -> std::io::Result<()> {
     log_info!(
         core,
         "listening on pipe {} (\\\\.\\pipe\\{})",
-        cfg.pipe_name,
-        cfg.pipe_name
+        server.cfg.pipe_name,
+        server.cfg.pipe_name
     );
 
     for conn in listener.incoming() {
         let conn = conn?;
-        let cfg = Arc::clone(&cfg);
+        let server = Arc::clone(&server);
         thread::spawn(move || {
             log_debug!(pipe, "connection accepted");
-            if let Err(e) = handle(&cfg, conn) {
+            if let Err(e) = handle(&server, conn) {
                 log_error!(pipe, "connection error: {}", e);
             }
         });
diff --git a/chusql-storage/src/btree.rs b/chusql-storage/src/btree.rs
index 2ec4503..5d4e536 100644
--- a/chusql-storage/src/btree.rs
+++ b/chusql-storage/src/btree.rs
@@ -3,100 +3,98 @@ use std::path::Path;
 
 use crate::page::{Page, PageFile, PageId};
 
-// 磁盘版 B+ 树：每个节点占一页，page 0 存文件头（魔数 + 页大小 + order + 根页号）。
-// 节点页布局（order = 一个节点最多几个孩子，来自配置）：
-//   [0]              节点类型：0=叶子，1=内部
-//   [1..3]           键数量 u16
-//   [3..11]          叶子的 next 页号 u64（内部保留）
-//   [12..12+K*8]     键：K = order-1 个 i64
-//   [后面]           叶子：K 个 u64 值；内部：order 个 u64 孩子页号
+// 磁盘 B+ 树：节点占一页，文件头记页大小与 order。
 
-/// 文件头放在这一页。
+// 布局常量
+/// 文件头放在第 0 页
 const META_PAGE: PageId = 0;
-/// 文件头魔数。
+/// 魔数，用来认出索引文件
 const META_MAGIC: &[u8; 4] = b"CBTR";
-/// 文件头里各字段的偏移。
+/// 文件头各字段的偏移
 const OFF_META_PAGE_SIZE: usize = 4;
 const OFF_META_ORDER: usize = 8;
 const OFF_META_ROOT: usize = 10;
 
-/// 节点类型标记。
+/// 节点类型标记
 const NODE_LEAF: u8 = 0;
 const NODE_INTERNAL: u8 = 1;
-/// 布局偏移。
+/// 节点内布局的偏移
 const OFF_TYPE: usize = 0;
 const OFF_COUNT: usize = 1;
 const OFF_NEXT: usize = 3;
 const OFF_KEYS: usize = 12;
 
-/// 一个 order 的节点占多少字节（内部节点最坏情况：order-1 个键 + order 个孩子）。
+// 容量计算
+/// 一个节点占多少字节
 fn node_bytes(order: usize) -> usize {
     OFF_KEYS + max_keys(order) * 8 + order * 8
 }
 
-/// 一个节点最多几个键。
+/// 最多几个键
 fn max_keys(order: usize) -> usize {
     order - 1
 }
 
-/// 键后面那片区域的起点。
+/// 值区域的起点
 fn off_payload(order: usize) -> usize {
     OFF_KEYS + max_keys(order) * 8
 }
 
-/// 这个 order 放得进 size 字节的页吗。
+/// 这个 order 放得进一页吗
 pub fn fits_in_page(page_size: usize, order: usize) -> bool {
     order >= 2 && node_bytes(order) <= page_size
 }
 
-/// 给定页大小，order 最大能取多少（解 12 + (order-1)*8 + order*8 <= page_size）。
+/// 一页最多几个孩子
 pub fn max_order(page_size: usize) -> usize {
     page_size.saturating_sub(4) / 16
 }
 
-/// 读一个 u8。
+// 小端读写
+/// 读一个 u8
 fn read_u8(p: &Page, off: usize) -> u8 {
     p.data[off]
 }
 
-/// 写一个 u8。
+/// 写一个 u8
 fn write_u8(p: &mut Page, off: usize, v: u8) {
     p.data[off] = v;
 }
 
-/// 读一个小端 u16。
+/// 读一个小端 u16
 fn read_u16(p: &Page, off: usize) -> u16 {
     u16::from_le_bytes([p.data[off], p.data[off + 1]])
 }
 
-/// 写一个小端 u16。
+/// 写一个小端 u16
 fn write_u16(p: &mut Page, off: usize, v: u16) {
     p.data[off..off + 2].copy_from_slice(&v.to_le_bytes());
 }
 
-/// 读一个小端 u32。
+/// 读一个小端 u32
 fn read_u32(p: &Page, off: usize) -> u32 {
     u32::from_le_bytes([p.data[off], p.data[off + 1], p.data[off + 2], p.data[off + 3]])
 }
 
-/// 写一个小端 u32。
+/// 写一个小端 u32
 fn write_u32(p: &mut Page, off: usize, v: u32) {
     p.data[off..off + 4].copy_from_slice(&v.to_le_bytes());
 }
 
-/// 读一个小端 u64。
+/// 读一个小端 u64
 fn read_u64(p: &Page, off: usize) -> u64 {
     let mut b = [0u8; 8];
     b.copy_from_slice(&p.data[off..off + 8]);
     u64::from_le_bytes(b)
 }
 
-/// 写一个小端 u64。
+/// 写一个小端 u64
 fn write_u64(p: &mut Page, off: usize, v: u64) {
     p.data[off..off + 8].copy_from_slice(&v.to_le_bytes());
 }
 
-/// 写文件头。
+// 文件头
+/// 写文件头
 fn write_meta(page: &mut Page, page_size: usize, order: usize, root: PageId) {
     page.zero();
     page.data[0..4].copy_from_slice(META_MAGIC);
@@ -105,7 +103,7 @@ fn write_meta(page: &mut Page, page_size: usize, order: usize, root: PageId) {
     write_u64(page, OFF_META_ROOT, root);
 }
 
-/// 检查文件头和当前配置是否一致（页大小 / order 改了就会对不上）。
+/// 校验文件头与配置
 fn check_meta(page: &Page, page_size: usize, order: usize) -> io::Result<()> {
     if page.data[0..4] != *META_MAGIC {
         return Err(io::Error::new(
@@ -127,7 +125,8 @@ fn check_meta(page: &Page, page_size: usize, order: usize) -> io::Result<()> {
     Ok(())
 }
 
-/// 一个节点在内存里的样子。
+// 节点编解码
+/// 节点在内存里的样子
 enum NodeData {
     Leaf {
         keys: Vec<i64>,
@@ -140,7 +139,7 @@ enum NodeData {
     },
 }
 
-/// 从一页里读出节点。
+/// 从一页读出节点
 fn read_node(p: &Page, order: usize) -> NodeData {
     let ty = read_u8(p, OFF_TYPE);
     let n = read_u16(p, OFF_COUNT) as usize;
@@ -167,7 +166,7 @@ fn read_node(p: &Page, order: usize) -> NodeData {
     }
 }
 
-/// 把节点写回一页（先清零，避免残留）。
+/// 把节点写回一页
 fn write_node(p: &mut Page, node: &NodeData, order: usize) {
     p.zero();
     let payload = off_payload(order);
@@ -196,7 +195,7 @@ fn write_node(p: &mut Page, node: &NodeData, order: usize) {
     }
 }
 
-/// 二分找 key 应该下探到的孩子下标。
+/// 二分选孩子
 fn child_index(keys: &[i64], key: i64) -> usize {
     let mut lo = 0;
     let mut hi = keys.len();
@@ -211,15 +210,21 @@ fn child_index(keys: &[i64], key: i64) -> usize {
     lo
 }
 
-/// 磁盘版 B+ 树。
+// B+ 树
+/// 磁盘 B+ 树
 pub struct DiskBTree {
     file: PageFile,
     order: usize,
 }
 
 impl DiskBTree {
-    /// 打开或新建索引文件；页大小 / order 和文件头里记的不一致就报错。
-    pub fn open<P: AsRef<Path>>(path: P, page_size: usize, order: usize) -> io::Result<Self> {
+    /// 打开或新建索引文件
+    pub fn open<P: AsRef<Path>>(
+            path: P,
+            page_size: usize,
+            order: usize,
+            pool_size: usize,
+        ) -> io::Result<Self> {
         if !fits_in_page(page_size, order) {
             return Err(io::Error::new(
                 io::ErrorKind::InvalidInput,
@@ -231,7 +236,7 @@ impl DiskBTree {
                 ),
             ));
         }
-        let mut file = PageFile::open(path, page_size)?;
+        let mut file = PageFile::with_options(path, page_size, pool_size)?;
         if file.num_pages()? == 0 {
             let mut meta = Page::new(META_PAGE, page_size);
             write_meta(&mut meta, page_size, order, 0);
@@ -243,26 +248,26 @@ impl DiskBTree {
         Ok(DiskBTree { file, order })
     }
 
-    /// 读根页号；0 表示空树。
+    /// 读根页号
     fn root(&mut self) -> io::Result<Option<PageId>> {
         let meta = self.file.read_page(META_PAGE)?;
         let r = read_u64(&meta, OFF_META_ROOT);
         Ok(if r == 0 { None } else { Some(r) })
     }
 
-    /// 写根页号。
+    /// 写根页号
     fn set_root(&mut self, r: Option<PageId>) -> io::Result<()> {
         let mut meta = self.file.read_page(META_PAGE)?;
         write_u64(&mut meta, OFF_META_ROOT, r.unwrap_or(0));
         self.file.write_page(&meta)
     }
 
-    /// 分配一个新页。
+    /// 分配新页
     fn alloc(&mut self) -> io::Result<PageId> {
         Ok(self.file.append_page()?.id)
     }
 
-    /// 清空整棵树：截断文件后重写文件头（根页号归零）。
+    /// 清空整棵树
     pub fn clear(&mut self) -> io::Result<()> {
         let page_size = self.file.page_size();
         self.file.truncate()?;
@@ -272,12 +277,12 @@ impl DiskBTree {
         Ok(())
     }
 
-    /// 空页，用来拼一个新节点。
+    /// 空页，用来拼节点
     fn new_page(&self, id: PageId) -> Page {
         Page::new(id, self.file.page_size())
     }
 
-    /// 按 key 找 value。
+    /// 按 key 找 value
     pub fn get(&mut self, key: i64) -> io::Result<Option<u64>> {
         match self.root()? {
             None => Ok(None),
@@ -285,7 +290,7 @@ impl DiskBTree {
         }
     }
 
-    /// 递归查找。
+    /// 递归查找
     fn get_rec(&mut self, page_id: PageId, key: i64) -> io::Result<Option<u64>> {
         let p = self.file.read_page(page_id)?;
         match read_node(&p, self.order) {
@@ -299,7 +304,7 @@ impl DiskBTree {
         }
     }
 
-    /// 插入 / 覆盖一个键值对。
+    /// 插入或覆盖
     pub fn insert(&mut self, key: i64, value: u64) -> io::Result<()> {
         match self.root()? {
             None => {
@@ -317,7 +322,6 @@ impl DiskBTree {
             Some(r) => {
                 let (_, split) = self.insert_rec(r, key, value)?;
                 if let Some((sep, right_id)) = split {
-                    // 根分裂：长高一层。
                     let root_id = self.alloc()?;
                     let node = NodeData::Internal {
                         keys: vec![sep],
@@ -334,7 +338,7 @@ impl DiskBTree {
         }
     }
 
-    /// 递归插入；返回可能上提的 (分隔键, 新右页号)。
+    /// 递归插入，可能上提
     fn insert_rec(
         &mut self,
         page_id: PageId,
@@ -358,7 +362,6 @@ impl DiskBTree {
                     self.file.write_page(&p2)?;
                     Ok((page_id, None))
                 } else {
-                    // 叶子分裂：右叶最小键复制上提。
                     let mid = keys.len() / 2;
                     let rkeys = keys.split_off(mid);
                     let rvalues = values.split_off(mid);
@@ -409,7 +412,6 @@ impl DiskBTree {
                             self.file.write_page(&p2)?;
                             Ok((page_id, None))
                         } else {
-                            // 内部节点分裂：中间键上提，不再保留原件。
                             let mid = keys.len() / 2;
                             let up = keys[mid];
                             let rkeys = keys.split_off(mid + 1);
@@ -441,7 +443,7 @@ impl DiskBTree {
         }
     }
 
-    /// 按 key 升序返回所有键值对。
+    /// 按键升序返回全部
     pub fn iter_all(&mut self) -> io::Result<Vec<(i64, u64)>> {
         let mut out = Vec::new();
         if let Some(r) = self.root()? {
@@ -450,7 +452,7 @@ impl DiskBTree {
         Ok(out)
     }
 
-    /// 中序遍历一棵子树。
+    /// 中序遍历
     fn walk(&mut self, page_id: PageId, out: &mut Vec<(i64, u64)>) -> io::Result<()> {
         let p = self.file.read_page(page_id)?;
         match read_node(&p, self.order) {
@@ -467,4 +469,10 @@ impl DiskBTree {
         }
         Ok(())
     }
+
+    /// 把脏页写回
+    pub fn flush(&mut self) -> io::Result<()> {
+        self.file.flush()
+    }
+
 }
diff --git a/chusql-storage/src/catalog.rs b/chusql-storage/src/catalog.rs
index 601e9f8..5188b9a 100644
--- a/chusql-storage/src/catalog.rs
+++ b/chusql-storage/src/catalog.rs
@@ -1,5 +1,3 @@
-//! 数据字典：记录每张表有哪些列、什么类型。
-//! 存在 data/catalog.json。insert 时自动补列，describe 时读回。
 
 use std::collections::BTreeMap;
 use std::io;
@@ -9,20 +7,27 @@ use serde::{Deserialize, Serialize};
 
 use crate::protocol::{ColumnType, Row, SchemaColumn};
 
-/// 一张表的 schema。
+// 数据字典：记每张表有哪些列、什么类型、多少行。
+
 #[derive(Debug, Clone, Default, Serialize, Deserialize)]
+/// 一张表的 schema
 pub struct TableSchema {
     pub columns: Vec<SchemaColumn>,
+    #[serde(default)]
+    pub row_count: u64,
 }
 
-/// 整个数据字典。
 #[derive(Debug, Default, Serialize, Deserialize)]
+/// 数据字典：表名到 schema
 pub struct Catalog {
     tables: BTreeMap<String, TableSchema>,
 }
 
+
+
 impl Catalog {
-    /// 从文件读；文件不存在返回空字典。
+    // 读取与保存
+    /// 从文件读；不存在给空字典
     pub fn load<P: AsRef<Path>>(path: P) -> io::Result<Self> {
         if !path.as_ref().exists() {
             return Ok(Catalog::default());
@@ -34,23 +39,25 @@ impl Catalog {
         serde_json::from_slice(&bytes).map_err(io::Error::other)
     }
 
-    /// 写回文件。
+    /// 写回文件
     pub fn save<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
         let bytes = serde_json::to_vec_pretty(self).map_err(io::Error::other)?;
         std::fs::write(path, bytes)
     }
 
-    /// 一张表的 schema；没有就返回 None。
+    // 查询
+    /// 一张表的 schema
     pub fn describe(&self, table: &str) -> Option<&TableSchema> {
         self.tables.get(table)
     }
 
-    /// catalog 里记录的所有表名。
+    /// 记录过的所有表名
     pub fn table_names(&self) -> Vec<String> {
         self.tables.keys().cloned().collect()
     }
 
-    /// 按一行数据补列；已有的列不动。
+    // 更新
+    /// 按一行数据补列
     pub fn ensure_columns(&mut self, table: &str, row: &Row) {
         let entry = self.tables.entry(table.to_string()).or_default();
         for (k, v) in row {
@@ -66,15 +73,74 @@ impl Catalog {
         }
     }
 
-    /// 按多行数据补列；replace_all 用。
+    /// 建表；已存在报错
+    pub fn create_table(&mut self, table: &str, columns: Vec<SchemaColumn>) -> io::Result<()> {
+        if self.tables.contains_key(table) {
+            return Err(io::Error::new(
+                io::ErrorKind::AlreadyExists,
+                format!("table already exists: {}", table),
+            ));
+        }
+        self.tables.insert(
+            table.to_string(),
+            TableSchema {
+                columns,
+                row_count: 0,
+            },
+        );
+        Ok(())
+    }
+
+    /// 按多行数据补列
     pub fn ensure_columns_from_rows(&mut self, table: &str, rows: &[Row]) {
         for r in rows {
             self.ensure_columns(table, r);
         }
     }
+    /// 记一次插入：补列 + 行数 +1
+    pub fn record_insert(&mut self, table: &str, row: &Row) {
+        let entry = self.tables.entry(table.to_string()).or_default();
+        for (k, v) in row {
+            if entry.columns.iter().any(|c| &c.name == k) {
+                continue;
+            }
+            if let Some(ty) = infer_type(v) {
+                entry.columns.push(SchemaColumn { name: k.clone(), ty });
+            }
+        }
+        entry.row_count += 1;
+    }
+
+    /// 记一次整表替换：列照补，行数重置
+    pub fn record_replace_all(&mut self, table: &str, rows: &[Row]) {
+        let entry = self.tables.entry(table.to_string()).or_default();
+        for r in rows {
+            for (k, v) in r {
+                if entry.columns.iter().any(|c| &c.name == k) {
+                    continue;
+                }
+                if let Some(ty) = infer_type(v) {
+                    entry.columns.push(SchemaColumn { name: k.clone(), ty });
+                }
+            }
+        }
+        entry.row_count = rows.len() as u64;
+    }
+
+    /// 删表
+    pub fn drop_table(&mut self, table: &str) -> io::Result<()> {
+        if self.tables.remove(table).is_none() {
+            return Err(io::Error::new(
+                io::ErrorKind::NotFound,
+                format!("unknown table: {}", table),
+            ));
+        }
+        Ok(())
+    }
 }
 
-/// 从 JSON 值推断列类型；不支持的类型返回 None。
+// 推断
+/// 由 JSON 值猜列类型
 fn infer_type(v: &serde_json::Value) -> Option<ColumnType> {
     match v {
         serde_json::Value::Number(_) => Some(ColumnType::Int),
diff --git a/chusql-storage/src/config.rs b/chusql-storage/src/config.rs
index 2f616e7..1a3893f 100644
--- a/chusql-storage/src/config.rs
+++ b/chusql-storage/src/config.rs
@@ -4,45 +4,50 @@ use serde::Deserialize;
 
 use crate::log::Level;
 
-// 配置：优先环境变量，其次 TOML 文件，最后内置默认值（下面写的就是默认值）。
-// 每个选项的来源都记在 Loaded::origins 里，server 启动时打进日志——读了哪个文件、
-// 哪些选项走了默认回退，一眼能看出来。
+// 配置：环境变量优先于 TOML，最后回退内置默认值。
 
-/// 默认配置文件名（相对当前工作目录）；可用 CHUSQL_CONFIG 指到别处。
+// 默认值
+/// 默认配置文件路径
 pub const DEFAULT_CONFIG_PATH: &str = "chusql-storage.toml";
 
-/// 默认页大小（字节）。
+/// 默认池容量（页数）
+pub const DEFAULT_POOL_SIZE: usize = 64;
+/// 默认页大小
 pub const DEFAULT_PAGE_SIZE: usize = 4096;
-/// 默认 B+ 树节点最大孩子数。
+/// 默认 B+ 树 order
 pub const DEFAULT_BTREE_ORDER: usize = 4;
-/// 默认数据目录。
+/// 默认数据目录
 pub const DEFAULT_DATA_DIR: &str = "data";
-/// 默认管道名。
+/// 默认管道名
 pub const DEFAULT_PIPE_NAME: &str = "chusql-storage";
-/// 默认日志等级。
+/// 默认日志等级
 pub const DEFAULT_LOG_LEVEL: &str = "info";
 
-/// 页大小允许的范围。
+/// 页大小允许范围
 const MIN_PAGE_SIZE: usize = 512;
 const MAX_PAGE_SIZE: usize = 65536;
-/// B+ 树节点至少要放得下 2 个键，分裂规则才成立。
+/// order 最小值
 const MIN_BTREE_ORDER: usize = 3;
 
-/// 生效的配置。
 #[derive(Debug, Clone, PartialEq, Eq)]
+// 配置
+/// 生效的配置
 pub struct Config {
     pub page_size: usize,
     pub btree_order: usize,
+    pub pool_size: usize,
     pub data_dir: PathBuf,
     pub pipe_name: String,
     pub log_level: Level,
 }
 
+/// 全默认值
 impl Default for Config {
     fn default() -> Self {
         Config {
             page_size: DEFAULT_PAGE_SIZE,
             btree_order: DEFAULT_BTREE_ORDER,
+            pool_size: DEFAULT_POOL_SIZE,
             data_dir: PathBuf::from(DEFAULT_DATA_DIR),
             pipe_name: DEFAULT_PIPE_NAME.to_string(),
             log_level: Level::Info,
@@ -50,8 +55,8 @@ impl Default for Config {
     }
 }
 
-/// 一个选项的来源。
 #[derive(Debug, Clone, PartialEq, Eq)]
+/// 一个选项的来源
 pub enum Origin {
     Default,
     File(PathBuf),
@@ -59,7 +64,7 @@ pub enum Origin {
 }
 
 impl Origin {
-    /// 日志里那一列怎么写。
+    /// 来源的文案
     pub fn describe(&self) -> String {
         match self {
             Origin::Default => "default".to_string(),
@@ -69,20 +74,22 @@ impl Origin {
     }
 }
 
-/// 生效配置 + 每个选项的来源。
 #[derive(Debug, Clone)]
+/// 配置 + 每项来源
 pub struct Loaded {
     pub config: Config,
     pub config_path: Option<PathBuf>,
     pub origins: Vec<(&'static str, String, Origin)>,
 }
 
-/// TOML 文件里的形状：字段全部可选，没写的就当"文件没提这一项"。
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+// 文件形状
+/// TOML 的形状（字段都可选）
 struct FileConfig {
     page: Option<FilePage>,
     btree: Option<FileBtree>,
+    buffer: Option<FileBuffer>,
     storage: Option<FileStorage>,
     server: Option<FileServer>,
     log: Option<FileLog>,
@@ -90,35 +97,48 @@ struct FileConfig {
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+/// [buffer] 段
+struct FileBuffer {
+    pool_size: Option<usize>,
+}
+
+#[derive(Debug, Default, Deserialize)]
+#[serde(deny_unknown_fields)]
+/// [page] 段
 struct FilePage {
     size: Option<usize>,
 }
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+/// [btree] 段
 struct FileBtree {
     order: Option<usize>,
 }
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+/// [storage] 段
 struct FileStorage {
     data_dir: Option<String>,
 }
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+/// [server] 段
 struct FileServer {
     pipe_name: Option<String>,
 }
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
+/// [log] 段
 struct FileLog {
     level: Option<String>,
 }
 
-/// 从真实环境加载：CHUSQL_CONFIG（或当前目录的默认文件）+ 环境变量覆盖。
+// 加载
+/// 按真实环境加载
 pub fn load() -> Result<Loaded, String> {
     let path = match std::env::var("CHUSQL_CONFIG") {
         Ok(p) if !p.trim().is_empty() => Some(PathBuf::from(p)),
@@ -137,7 +157,7 @@ pub fn load() -> Result<Loaded, String> {
     resolve(text.as_deref(), path, &|k| std::env::var(k).ok())
 }
 
-/// 解析 TOML 文本 + 套环境变量覆盖；测试直接调这个，不碰真实环境。
+/// 解析文本并套环境变量
 pub fn resolve(
     text: Option<&str>,
     path: Option<PathBuf>,
@@ -180,6 +200,18 @@ pub fn resolve(
                 .map_err(|_| format!("not a number: {}", s))
         },
     )?;
+    let (pool_size, pool_origin) = pick(
+        "CHUSQL_POOL_SIZE",
+        file.buffer.and_then(|b| b.pool_size),
+        DEFAULT_POOL_SIZE,
+        &file_origin,
+        env,
+        |s| {
+            s.trim()
+                .parse::<usize>()
+                .map_err(|_| format!("not a number: {}", s))
+        },
+    )?;
     let (data_dir, dir_origin) = pick(
         "CHUSQL_DATA_DIR",
         file.storage.and_then(|s| s.data_dir),
@@ -214,10 +246,13 @@ pub fn resolve(
         return Err("server.pipe_name must not be empty".to_string());
     }
     validate_layout(page_size, btree_order)?;
-
+    if pool_size == 0 {
+        return Err("buffer.pool_size must be at least 1".to_string());
+    }
     let origins = vec![
         ("page.size", page_size.to_string(), page_origin),
         ("btree.order", btree_order.to_string(), order_origin),
+        ("buffer.pool_size", pool_size.to_string(), pool_origin),    // 新增
         ("storage.data_dir", data_dir.clone(), dir_origin),
         ("server.pipe_name", pipe_name.clone(), pipe_origin),
         ("log.level", log_level.name().to_string(), log_origin),
@@ -227,6 +262,7 @@ pub fn resolve(
         config: Config {
             page_size,
             btree_order,
+            pool_size,
             data_dir: PathBuf::from(data_dir),
             pipe_name,
             log_level,
@@ -236,7 +272,7 @@ pub fn resolve(
     })
 }
 
-/// 取一个选项：环境变量 → 配置文件 → 默认值，并记下它从哪来。
+/// 取一项：env -> 文件 -> 默认
 fn pick<T: Clone>(
     env_key: &'static str,
     file_value: Option<T>,
@@ -255,7 +291,8 @@ fn pick<T: Clone>(
     Ok((default, Origin::Default))
 }
 
-/// 检查选项本身和选项之间是否说得通。
+// 校验
+/// 检查选项是否自洽
 fn validate_layout(page_size: usize, btree_order: usize) -> Result<(), String> {
     if !(MIN_PAGE_SIZE..=MAX_PAGE_SIZE).contains(&page_size) || !page_size.is_power_of_two() {
         return Err(format!(
diff --git a/chusql-storage/src/heap.rs b/chusql-storage/src/heap.rs
index 1cb87eb..ebb6733 100644
--- a/chusql-storage/src/heap.rs
+++ b/chusql-storage/src/heap.rs
@@ -6,71 +6,68 @@ use crate::page::PageId;
 use crate::page::{Page, PageFile};
 use crate::protocol::Row;
 
-// 堆表：把行按插入顺序塞进页里，支持全表扫描。页大小由配置给（默认 4096）。
-// 页内布局（slotted page）：
-//   [0..2]  slot_count: u16（小端）
-//   [2..]   槽位目录，每槽 8 字节：offset u32 + len u32
-//   [中间]  空闲空间
-//   [页尾]  行数据，从后往前长
-// 删除：把槽位的 len 置 0，数据不动（vacuum 以后再说）。
+// 堆表：行按插入顺序进页，支持全表扫描与按索引取行。
 
-/// 页头：slot_count 占 2 字节。
+// 页内布局
+/// 页头：slot_count 占 2 字节
 const HEADER_SIZE: usize = 2;
-/// 一个槽位占 8 字节：offset(u32) + len(u32)。
+/// 一个槽位占 8 字节
 const SLOT_SIZE: usize = 8;
-/// 槽位目录起点。
+/// 槽位目录起点
 const SLOT_DIR_START: usize = HEADER_SIZE;
 
-/// 从字节里读一个小端 u16。
+/// 读一个小端 u16
 fn read_u16(buf: &[u8], off: usize) -> u16 {
     u16::from_le_bytes([buf[off], buf[off + 1]])
 }
 
-/// 往字节里写一个小端 u16。
+/// 写一个小端 u16
 fn write_u16(buf: &mut [u8], off: usize, v: u16) {
     buf[off..off + 2].copy_from_slice(&v.to_le_bytes());
 }
 
-/// 从字节里读一个小端 u32。
+/// 读一个小端 u32
 fn read_u32(buf: &[u8], off: usize) -> u32 {
     u32::from_le_bytes([buf[off], buf[off + 1], buf[off + 2], buf[off + 3]])
 }
 
-/// 往字节里写一个小端 u32。
+/// 写一个小端 u32
 fn write_u32(buf: &mut [u8], off: usize, v: u32) {
     buf[off..off + 4].copy_from_slice(&v.to_le_bytes());
 }
 
-/// 一个 (页号, 槽位号) 打包成一个 u64。页号高 48 位，槽位号低 16 位。
+// 索引位置
+/// (页号, 槽位号) 打包成 u64
 fn pack_position(page_id: PageId, slot: u16) -> u64 {
     (page_id << 16) | (slot as u64)
 }
 
-/// 从 u64 解回 (页号, 槽位号)。
+/// 从 u64 解回 (页号, 槽位号)
 fn unpack_position(v: u64) -> (PageId, u16) {
     (v >> 16, (v & 0xFFFF) as u16)
 }
 
-/// 页内操作：不管文件，只管一页里的字节。
+// 页内操作
+/// 只管一页里的字节
 pub struct HeapPage;
 
 impl HeapPage {
-    /// 这一页里有多少个槽位。
+    /// 这一页有几个槽位
     pub fn slot_count(page: &Page) -> u16 {
         read_u16(&page.data, 0)
     }
 
-    /// 改写槽位数量。
+    /// 改写槽位数量
     fn set_slot_count(page: &mut Page, v: u16) {
         write_u16(&mut page.data, 0, v);
     }
 
-    /// 空闲空间下界：槽位目录的末尾。
+    /// 空闲空间下界
     fn free_start(page: &Page) -> usize {
         SLOT_DIR_START + (Self::slot_count(page) as usize) * SLOT_SIZE
     }
 
-    /// 空闲空间上界：所有存活行里最靠前的那个字节偏移（没存活行时就是页尾）。
+    /// 空闲空间上界
     fn free_end(page: &Page) -> usize {
         let n = Self::slot_count(page);
         let mut min_off = page.data.len() as u32;
@@ -85,7 +82,7 @@ impl HeapPage {
         min_off as usize
     }
 
-    /// 试插一行：成功返回槽位号，放不下返回 None。
+    /// 试插一行，放不下返回 None
     pub fn insert_tuple(page: &mut Page, tuple: &[u8]) -> Option<u16> {
         let n = Self::slot_count(page);
         let free_start = Self::free_start(page);
@@ -95,11 +92,9 @@ impl HeapPage {
             return None;
         }
 
-        // 行数据紧贴已有数据前面
         let tuple_off = free_end - tuple.len();
         page.data[tuple_off..tuple_off + tuple.len()].copy_from_slice(tuple);
 
-        // 追加槽位
         let slot_off = SLOT_DIR_START + (n as usize) * SLOT_SIZE;
         write_u32(&mut page.data, slot_off, tuple_off as u32);
         write_u32(&mut page.data, slot_off + 4, tuple.len() as u32);
@@ -108,7 +103,7 @@ impl HeapPage {
         Some(n)
     }
 
-    /// 读槽位里的行字节；槽位不存在或已删除返回 None。
+    /// 读槽位里的行字节
     pub fn get_tuple(page: &Page, slot: u16) -> Option<Vec<u8>> {
         let n = Self::slot_count(page);
         if slot >= n {
@@ -123,46 +118,52 @@ impl HeapPage {
         Some(page.data[off..off + len].to_vec())
     }
 
-    /// 所有槽位号（含已删除的）。
+    /// 所有槽位号
     pub fn iter_slots(page: &Page) -> Vec<u16> {
         (0..Self::slot_count(page)).collect()
     }
 }
 
-/// 堆表：一个文件 = 若干页，顺序追加行。
+// 堆表
+/// 一个文件 = 若干页
 pub struct HeapTable {
     file: PageFile,
     index: Option<DiskBTree>,
 }
 
 impl HeapTable {
-    /// 打开（或创建）一张堆表。
-    pub fn open<P: AsRef<Path>>(path: P, page_size: usize) -> io::Result<Self> {
-        Ok(HeapTable {
-            file: PageFile::open(path, page_size)?,
+    /// 打开表（不带索引）
+    pub fn open<P: AsRef<Path>>(
+        path: P,
+        page_size: usize,
+        pool_size: usize,
+    ) -> io::Result<Self> {
+         Ok(HeapTable {
+            file: PageFile::with_options(path, page_size, pool_size)?,
             index: None,
         })
     }
 
-    /// 打开带 B+ 树索引的表；索引文件不存在会自动建。
+    /// 打开表 + 索引
     pub fn open_indexed<P: AsRef<Path>, Q: AsRef<Path>>(
         path: P,
         index_path: Q,
         page_size: usize,
         btree_order: usize,
+        pool_size: usize,
     ) -> io::Result<Self> {
         Ok(HeapTable {
-            file: PageFile::open(path, page_size)?,
-            index: Some(DiskBTree::open(index_path, page_size, btree_order)?),
+            file: PageFile::with_options(path, page_size, pool_size)?,
+            index: Some(DiskBTree::open(index_path, page_size, btree_order, pool_size)?),
         })
     }
 
-    /// 插入一行；不更新索引。
+    /// 插入一行，不更新索引
     pub fn insert(&mut self, row: &Row) -> io::Result<()> {
         self.insert_returning_position(row).map(|_| ())
     }
 
-    /// 插入一行并返回它的 (页号, 槽位号)。
+    /// 插入并返回行位置
     pub fn insert_returning_position(&mut self, row: &Row) -> io::Result<(PageId, u16)> {
         let tuple = serde_json::to_vec(row).map_err(io::Error::other)?;
 
@@ -190,7 +191,7 @@ impl HeapTable {
         Ok((page_id, slot))
     }
 
-    /// 插入一行，并把 (key, 位置) 写进索引。
+    /// 插入一行并写索引
     pub fn insert_keyed(&mut self, row: &Row, key: i64) -> io::Result<()> {
         let (page_id, slot) = self.insert_returning_position(row)?;
         if let Some(idx) = &mut self.index {
@@ -199,7 +200,7 @@ impl HeapTable {
         Ok(())
     }
 
-    /// 按索引键取一行；没索引或键不存在返回 None。
+    /// 按索引键取一行
     pub fn get_by_key(&mut self, key: i64) -> io::Result<Option<Row>> {
         let pos = match &mut self.index {
             None => return Ok(None),
@@ -212,7 +213,7 @@ impl HeapTable {
         self.read_at(page_id, slot)
     }
 
-    /// 按 (页号, 槽位号) 读一行。
+    /// 按位置读一行
     pub fn read_at(&mut self, page_id: PageId, slot: u16) -> io::Result<Option<Row>> {
         let p = self.file.read_page(page_id)?;
         match HeapPage::get_tuple(&p, slot) {
@@ -224,7 +225,7 @@ impl HeapTable {
         }
     }
 
-    /// 全表扫描：按页顺序、按槽位顺序返回所有行。
+    /// 全表扫描
     pub fn scan(&mut self) -> io::Result<Vec<Row>> {
         let n = self.file.num_pages()?;
         let mut rows = Vec::new();
@@ -241,8 +242,7 @@ impl HeapTable {
         Ok(rows)
     }
 
-    /// 整表改写：清空堆表和索引，再把新行逐行插回去。
-    /// 行里有整数 id 就顺手重建索引 —— 堆表位置变了，旧索引必须作废，否则会按老位置读出别的行。
+    /// 整表改写并重建索引
     pub fn replace_all(&mut self, rows: &[Row]) -> io::Result<()> {
         self.file.truncate()?;
         if let Some(idx) = &mut self.index {
@@ -256,9 +256,27 @@ impl HeapTable {
         }
         Ok(())
     }
+
+    /// 把脏页写回
+    pub fn flush(&mut self) -> io::Result<()> {
+        if let Some(idx) = &mut self.index {
+            idx.flush()?;
+        }
+        self.file.flush()
+    }
+
+    // 缓冲池统计
+    /// 当前缓存页数
+    pub fn cached_pages(&self) -> usize { self.file.cached_pages() }
+    /// 命中次数
+    pub fn hits(&self) -> u64 { self.file.hits() }
+    /// 未命中次数
+    pub fn misses(&self) -> u64 { self.file.misses() }
+    /// 命中率
+    pub fn hit_rate(&self) -> f64 { self.file.hit_rate() }
 }
 
-/// 一行里的索引键：id 列是整数就用它（和 Haskell 侧"主键列叫 id"的约定一致）。
+/// 取行里的 id 作索引键
 fn row_key(row: &Row) -> Option<i64> {
     match row.get("id") {
         Some(serde_json::Value::Number(n)) => n.as_i64(),
diff --git a/chusql-storage/src/lib.rs b/chusql-storage/src/lib.rs
index ef44d7a..1d412bd 100644
--- a/chusql-storage/src/lib.rs
+++ b/chusql-storage/src/lib.rs
@@ -1,4 +1,4 @@
-// 存储层库入口：对外暴露 page / protocol / heap / btree / config / log（server 与集成测试都从这里引）。
+// 存储层库入口：对外暴露下面这些模块，服务与集成测试都从这里引。
 
 pub mod btree;
 pub mod config;
diff --git a/chusql-storage/src/log.rs b/chusql-storage/src/log.rs
index 8ed6fbb..e360443 100644
--- a/chusql-storage/src/log.rs
+++ b/chusql-storage/src/log.rs
@@ -3,23 +3,21 @@ use std::io::{IsTerminal, Write};
 use std::sync::atomic::{AtomicU8, Ordering};
 use std::sync::OnceLock;
 
-// 极简日志：等级存在一个原子变量里，被关掉的等级只花一次原子读——不求值参数、不做格式化。
-// 行格式：[等级 本地日期时间] [来源] 消息
-//   - ERROR 加粗红、WARN 加粗橙、DEBUG 加粗不变色（只在 stderr 是终端时着色，重定向到文件时是纯文本）
-//   - 来源区分 core（服务自身：启动、配置）和 pipe（由管道请求触发）
-// 等级由配置文件的 log.level 或环境变量 CHUSQL_LOG 决定。
+// 极简日志：等级用原子变量，关掉的等级只花一次原子读。
 
-/// 转义序列收尾。
+// 颜色
+/// 转义序列收尾
 const RESET: &str = "\u{1b}[0m";
-/// 加粗红（ERROR）。
+/// 加粗红（ERROR）
 const BOLD_RED: &str = "\u{1b}[1m\u{1b}[31m";
-/// 加粗橙（WARN）：256 色里的 208 号。
+/// 加粗橙（WARN）
 const BOLD_ORANGE: &str = "\u{1b}[1m\u{1b}[38;5;208m";
-/// 只加粗（DEBUG）。
+/// 只加粗（DEBUG）
 const BOLD: &str = "\u{1b}[1m";
 
-/// 日志等级；Off 表示全关。
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+// 等级与来源
+/// 日志等级
 pub enum Level {
     Off,
     Error,
@@ -28,15 +26,15 @@ pub enum Level {
     Debug,
 }
 
-/// 日志来源：core = 服务自身，pipe = 由管道请求触发。
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// 来源：服务自身或管道请求
 pub enum Channel {
     Core,
     Pipe,
 }
 
 impl Channel {
-    /// 日志行里的来源标签。
+    /// 来源标签
     fn tag(self) -> &'static str {
         match self {
             Channel::Core => "core",
@@ -46,7 +44,7 @@ impl Channel {
 }
 
 impl Level {
-    /// 解析等级名（大小写不敏感）。
+    /// 解析等级名
     pub fn parse(s: &str) -> Option<Level> {
         match s.trim().to_ascii_lowercase().as_str() {
             "off" => Some(Level::Off),
@@ -58,7 +56,7 @@ impl Level {
         }
     }
 
-    /// 等级名（写日志和写配置说明用）。
+    /// 等级名
     pub fn name(self) -> &'static str {
         match self {
             Level::Off => "off",
@@ -69,7 +67,7 @@ impl Level {
         }
     }
 
-    /// 日志行里的标签，固定 5 字符宽，方便对齐。
+    /// 行里的等级标签
     fn tag(self) -> &'static str {
         match self {
             Level::Error => "ERROR",
@@ -79,7 +77,7 @@ impl Level {
         }
     }
 
-    /// 这个等级要不要着色（INFO 不着色）。
+    /// 等级的颜色
     fn color(self) -> &'static str {
         match self {
             Level::Error => BOLD_RED,
@@ -90,29 +88,28 @@ impl Level {
     }
 }
 
-/// 当前等级，默认 info。
 static LEVEL: AtomicU8 = AtomicU8::new(Level::Info as u8);
 
-/// stderr 是不是终端（决定要不要着色），只问一次。
 static COLOR: OnceLock<bool> = OnceLock::new();
 
-/// 设置全局等级。
+// 写入
+/// 设置全局等级
 pub fn set_level(level: Level) {
     LEVEL.store(level as u8, Ordering::Relaxed);
 }
 
-/// 这个等级要不要输出——热路径上只走这一步（一次原子读 + 比较）。
 #[inline]
+/// 这个等级要不要输出
 pub fn enabled(level: Level) -> bool {
     level as u8 <= LEVEL.load(Ordering::Relaxed)
 }
 
-/// 启动时调一次：Windows 上给 stderr 打开 VT 处理，让 ANSI 颜色能被认识。
+/// 启动时调一次
 pub fn init() {
     enable_vt();
 }
 
-/// 写出一行；只在 enabled 为真时调用。
+/// 写出一行
 pub fn write(channel: Channel, level: Level, args: fmt::Arguments) {
     let msg = args.to_string();
     let line = render(level, channel, color_enabled(), &now(), &msg);
@@ -121,7 +118,7 @@ pub fn write(channel: Channel, level: Level, args: fmt::Arguments) {
     let _ = writeln!(out, "{}", line);
 }
 
-/// stderr 是终端才着色；CHUSQL_LOG_COLOR=always / never 可以强制开关。
+/// 是否着色（终端或强制）
 fn color_enabled() -> bool {
     *COLOR.get_or_init(|| match std::env::var("CHUSQL_LOG_COLOR").as_deref().map(str::trim) {
         Ok("always") | Ok("yes") | Ok("1") => true,
@@ -130,7 +127,7 @@ fn color_enabled() -> bool {
     })
 }
 
-/// 拼一行：[等级 时间] [来源] 消息。纯函数，方便测试。
+/// 拼一行（纯函数，可测）
 fn render(level: Level, channel: Channel, color: bool, stamp: &Stamp, msg: &str) -> String {
     let tag = level.tag();
     let paint = level.color();
@@ -142,8 +139,9 @@ fn render(level: Level, channel: Channel, color: bool, stamp: &Stamp, msg: &str)
     format!("[{} {}] [{}] {}", level_text, stamp, channel.tag(), msg)
 }
 
-/// 一个本地日期时间。
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+// 时间
+/// 本地日期时间
 pub struct Stamp {
     pub year: u16,
     pub month: u16,
@@ -154,6 +152,7 @@ pub struct Stamp {
     pub milli: u16,
 }
 
+/// 格式：年-月-日 时:分:秒.毫秒
 impl fmt::Display for Stamp {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
@@ -164,7 +163,7 @@ impl fmt::Display for Stamp {
     }
 }
 
-/// 当前本地时间：Windows 上走 kernel32::GetLocalTime。
+/// 当前本地时间（Windows）
 #[cfg(windows)]
 fn now() -> Stamp {
     #[repr(C)]
@@ -206,7 +205,7 @@ fn now() -> Stamp {
     }
 }
 
-/// 当前时间：其他平台没有取本地时区的零依赖办法，退回 UTC。
+/// 当前时间（其他平台用 UTC）
 #[cfg(not(windows))]
 fn now() -> Stamp {
     let d = std::time::SystemTime::now()
@@ -225,7 +224,7 @@ fn now() -> Stamp {
     }
 }
 
-/// 把"距 1970-01-01 的天数"换算成 (年, 月, 日)：非 Windows 平台算时间用，单元测试也走这里。
+/// 天数换算成日期
 pub fn civil_from_days(days: i64) -> (i64, u16, u16) {
     let z = days + 719_468;
     let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
@@ -239,7 +238,8 @@ pub fn civil_from_days(days: i64) -> (i64, u16, u16) {
     (y + i64::from(month <= 2), month, day)
 }
 
-/// Windows：打开 stderr 的 VT 处理。
+// 终端
+/// 打开 Windows 的 VT 处理
 #[cfg(windows)]
 fn enable_vt() {
     #[link(name = "kernel32")]
@@ -249,9 +249,7 @@ fn enable_vt() {
         fn SetConsoleMode(handle: *mut core::ffi::c_void, mode: u32) -> i32;
     }
 
-    /// STD_ERROR_HANDLE：-12 的无符号写法。
     const STD_ERROR_HANDLE: u32 = 0xFFFF_FFF4;
-    /// 让控制台认识 ANSI 转义序列。
     const ENABLE_VIRTUAL_TERMINAL_PROCESSING: u32 = 0x0004;
 
     unsafe {
@@ -263,11 +261,12 @@ fn enable_vt() {
     }
 }
 
-/// 非 Windows：不用做任何事。
+/// 其他平台什么都不用做
 #[cfg(not(windows))]
 fn enable_vt() {}
 
-/// 打一条 debug 日志（关掉时只花一次原子读）。
+// 宏
+/// debug 日志
 #[macro_export]
 macro_rules! log_debug {
     (core, $($arg:tt)*) => {
@@ -278,7 +277,7 @@ macro_rules! log_debug {
     };
 }
 
-/// 打一条 info 日志。
+/// info 日志
 #[macro_export]
 macro_rules! log_info {
     (core, $($arg:tt)*) => {
@@ -289,7 +288,7 @@ macro_rules! log_info {
     };
 }
 
-/// 打一条 warn 日志。
+/// warn 日志
 #[macro_export]
 macro_rules! log_warn {
     (core, $($arg:tt)*) => {
@@ -300,7 +299,7 @@ macro_rules! log_warn {
     };
 }
 
-/// 打一条 error 日志。
+/// error 日志
 #[macro_export]
 macro_rules! log_error {
     (core, $($arg:tt)*) => {
@@ -311,7 +310,7 @@ macro_rules! log_error {
     };
 }
 
-/// 上面四个宏的公共部分：先看等级，再看要不要真的写。内部用，别直接调。
+/// 四个宏的公共部分
 #[doc(hidden)]
 #[macro_export]
 macro_rules! log_line {
@@ -326,7 +325,6 @@ macro_rules! log_line {
 mod tests {
     use super::*;
 
-    /// 天数换算日期：几个已知点 + 两次闰年的 2 月 29 日。
     #[test]
     fn civil_from_days_known_dates() {
         assert_eq!(civil_from_days(0), (1970, 1, 1));
@@ -336,7 +334,6 @@ mod tests {
         assert_eq!(civil_from_days(19_782), (2024, 2, 29));
     }
 
-    /// 行格式：等级 + 本地日期时间 + 来源 + 消息，等级该粗的粗、该色的色。
     #[test]
     fn render_has_time_channel_and_colors() {
         let stamp = Stamp {
@@ -367,7 +364,6 @@ mod tests {
         );
     }
 
-    /// 关掉颜色时整行必须是纯文本（重定向到文件时用）。
     #[test]
     fn render_without_color_is_plain() {
         let stamp = Stamp {
diff --git a/chusql-storage/src/page.rs b/chusql-storage/src/page.rs
index 1e1514b..763ad3c 100644
--- a/chusql-storage/src/page.rs
+++ b/chusql-storage/src/page.rs
@@ -1,23 +1,26 @@
+use std::collections::{HashMap, HashSet, VecDeque};
 use std::fs::{File, OpenOptions};
 use std::io::{self, Read, Seek, SeekFrom, Write};
 use std::path::Path;
 
-// 页管理：数据库文件按固定大小的页组织，页大小由配置给（默认 4096，见 config.rs）。
-// 只负责"按页号读 / 写"，不理解页里的内容 —— 内容怎么解释由上层（堆表 / B+ 树 / WAL）决定。
-// 页号从 0 开始，第 n 页在文件中的偏移是 n * page_size。
+// 页管理：定长页的读写，外加一层页缓冲池。
 
-/// 页号：从 0 开始。u64 足够大，不用担心中途用完。
+// 页
+/// 页号：从 0 开始
 pub type PageId = u64;
 
-/// 一页：固定 page_size 字节，外加自己的页号。
+/// 缓冲池默认容量（页数）
+pub const DEFAULT_POOL_SIZE: usize = 64;
+
 #[derive(Debug, Clone)]
+/// 一页：定长字节 + 页号
 pub struct Page {
     pub id: PageId,
     pub data: Vec<u8>,
 }
 
 impl Page {
-    /// 新建一页，内容全 0。
+    /// 新建一页，全 0
     pub fn new(id: PageId, size: usize) -> Self {
         Page {
             id,
@@ -25,46 +28,118 @@ impl Page {
         }
     }
 
-    /// 清零。复用时先清空，避免残留旧数据。
+    /// 清零
     pub fn zero(&mut self) {
         self.data.fill(0);
     }
 }
 
-/// 页文件：负责把 Page 落到磁盘上（不做缓存，每次读写都直接 syscall；缓冲池是后面的阶段）。
 #[derive(Debug)]
+/// 页文件：定长页读写 + 页缓存
 pub struct PageFile {
     file: File,
     page_size: usize,
+    capacity: usize,
+    cache: HashMap<PageId, Page>,
+    order: VecDeque<PageId>,
+    dirty: HashSet<PageId>,
+    hits: u64,
+    misses: u64,
 }
 
 impl PageFile {
-    /// 打开（或创建）一个页文件；页大小由配置传进来。
+    /// 打开页文件（默认池容量）
     pub fn open<P: AsRef<Path>>(path: P, page_size: usize) -> io::Result<Self> {
+        Self::with_options(path, page_size, DEFAULT_POOL_SIZE)
+    }
+
+    /// 打开页文件并指定池容量
+    pub fn with_options<P: AsRef<Path>>(
+        path: P,
+        page_size: usize,
+        capacity: usize,
+    ) -> io::Result<Self> {
         let file = OpenOptions::new()
             .read(true)
             .write(true)
             .create(true)
             .truncate(false)
             .open(path)?;
-        Ok(PageFile { file, page_size })
+        Ok(PageFile {
+            file,
+            page_size,
+            capacity,
+            cache: HashMap::new(),
+            order: VecDeque::new(),
+            dirty: HashSet::new(),
+            hits: 0,
+            misses: 0,
+        })
     }
 
-    /// 这个文件的页大小。
+    /// 页大小
     pub fn page_size(&self) -> usize {
         self.page_size
     }
 
-    /// 读取指定页号的页；页号超出文件末尾时返回 UnexpectedEof。
-    pub fn read_page(&mut self, id: PageId) -> io::Result<Page> {
-        let mut data = vec![0u8; self.page_size];
-        self.file.seek(SeekFrom::Start(id * self.page_size as u64))?;
-        self.file.read_exact(&mut data)?;
-        Ok(Page { id, data })
+// 缓冲池
+    /// 池容量（页数）
+    pub fn capacity(&self) -> usize {
+        self.capacity
     }
 
-    /// 写入一页。若页号超出当前文件末尾，文件会自动扩展。
-    pub fn write_page(&mut self, page: &Page) -> io::Result<()> {
+    /// 当前缓存了多少页
+    pub fn cached_pages(&self) -> usize {
+        self.cache.len()
+    }
+
+    /// 命中次数
+    pub fn hits(&self) -> u64 {
+        self.hits
+    }
+
+    /// 未命中次数
+    pub fn misses(&self) -> u64 {
+        self.misses
+    }
+
+    /// 命中率
+    pub fn hit_rate(&self) -> f64 {
+        let total = self.hits + self.misses;
+        if total == 0 {
+            0.0
+        } else {
+            self.hits as f64 / total as f64
+        }
+    }
+
+
+    /// 标记为最近使用
+    fn touch(&mut self, id: PageId) {
+        if let Some(pos) = self.order.iter().position(|&x| x == id) {
+            self.order.remove(pos);
+        }
+        self.order.push_back(id);
+    }
+
+    /// 淘汰一个最冷的页
+    fn evict_one(&mut self) -> io::Result<bool> {
+        while let Some(victim) = self.order.pop_front() {
+            if let Some(p) = self.cache.get(&victim) {
+                if self.dirty.contains(&victim) {
+                    let p = p.clone();
+                    self.write_raw(&p)?;
+                    self.dirty.remove(&victim);
+                }
+                self.cache.remove(&victim);
+                return Ok(true);
+            }
+        }
+        Ok(false)
+    }
+
+    /// 直接写文件
+    fn write_raw(&mut self, page: &Page) -> io::Result<()> {
         if page.data.len() != self.page_size {
             return Err(io::Error::new(
                 io::ErrorKind::InvalidInput,
@@ -77,12 +152,58 @@ impl PageFile {
         }
         self.file
             .seek(SeekFrom::Start(page.id * self.page_size as u64))?;
-        self.file.write_all(&page.data)?;
-        self.file.flush()?;
+        self.file.write_all(&page.data)
+    }
+
+    /// 直接从文件读
+    fn read_raw(&mut self, id: PageId) -> io::Result<Page> {
+        let mut data = vec![0u8; self.page_size];
+        self.file.seek(SeekFrom::Start(id * self.page_size as u64))?;
+        self.file.read_exact(&mut data)?;
+        Ok(Page { id, data })
+    }
+
+
+    /// 读一页（走缓存）
+    pub fn read_page(&mut self, id: PageId) -> io::Result<Page> {
+        if let Some(p) = self.cache.get(&id) {
+            let p = p.clone();
+            self.hits += 1;
+            self.touch(id);
+            return Ok(p);
+        }
+        self.misses += 1;
+        let p = self.read_raw(id)?;
+        if self.cache.len() >= self.capacity {
+            self.evict_one()?;
+        }
+        self.cache.insert(id, p.clone());
+        self.order.push_back(id);
+        Ok(p)
+    }
+
+    /// 写一页（走缓存）
+    pub fn write_page(&mut self, page: &Page) -> io::Result<()> {
+        if page.data.len() != self.page_size {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                format!(
+                    "page has {} bytes, this file uses {}",
+                    page.data.len(),
+                    self.page_size
+                ),
+            ));
+        }
+        if self.cache.len() >= self.capacity && !self.cache.contains_key(&page.id) {
+            self.evict_one()?;
+        }
+        self.cache.insert(page.id, page.clone());
+        self.dirty.insert(page.id);
+        self.touch(page.id);
         Ok(())
     }
 
-    /// 在文件末尾追加一页，返回新页的页号。
+    /// 末尾追加一页
     pub fn append_page(&mut self) -> io::Result<Page> {
         let id = self.num_pages()?;
         let page = Page::new(id, self.page_size);
@@ -90,7 +211,7 @@ impl PageFile {
         Ok(page)
     }
 
-    /// 当前文件里有多少页；长度不是页大小整数倍，说明页大小和文件对不上。
+    /// 文件里有多少页
     pub fn num_pages(&mut self) -> io::Result<PageId> {
         let len = self.file.metadata()?.len();
         let size = self.page_size as u64;
@@ -103,18 +224,50 @@ impl PageFile {
                 ),
             ));
         }
-        Ok(len / size)
+        let on_disk = len / size;
+        let cached_max = self
+            .cache
+            .keys()
+            .copied()
+            .max()
+            .map(|m| m + 1)
+            .unwrap_or(0);
+        Ok(on_disk.max(cached_max))
     }
 
-    /// 强制把文件缓冲刷到磁盘。写入关键路径时用。
+    /// 把脏页写回磁盘
+    pub fn flush(&mut self) -> io::Result<()> {
+        let dirty: Vec<PageId> = self.dirty.iter().copied().collect();
+        for id in dirty {
+            if let Some(p) = self.cache.get(&id) {
+                let p = p.clone();
+                self.write_raw(&p)?;
+            }
+        }
+        self.file.sync_all()?;
+        self.dirty.clear();
+        Ok(())
+    }
+
+    /// flush 之后 fsync
     pub fn sync(&mut self) -> io::Result<()> {
-        self.file.sync_all()
+        self.flush()
     }
 
-    /// 清空文件，游标归零。
+    /// 清空文件
     pub fn truncate(&mut self) -> io::Result<()> {
+        self.cache.clear();
+        self.order.clear();
+        self.dirty.clear();
         self.file.set_len(0)?;
         self.file.seek(SeekFrom::Start(0))?;
         Ok(())
     }
 }
+
+    /// 退出前把脏页写回
+impl Drop for PageFile {
+    fn drop(&mut self) {
+        let _ = self.flush();
+    }
+}
diff --git a/chusql-storage/src/protocol.rs b/chusql-storage/src/protocol.rs
index 220b8ca..44e6bac 100644
--- a/chusql-storage/src/protocol.rs
+++ b/chusql-storage/src/protocol.rs
@@ -1,30 +1,30 @@
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
-// 协议定义：Haskell ↔ Rust 之间那条"行分隔 JSON"消息的类型（请求 / 响应）。
+// 协议：Haskell 与 Rust 之间的请求 / 响应类型。
 
-/// 一行：列名到 JSON 值的映射。
+/// 一行：列名到 JSON 值
 pub type Row = HashMap<String, serde_json::Value>;
 
-/// 列类型；跟 Haskell 侧 TInt / TStr / TBool 对应。
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(rename_all = "lowercase")]
+/// 列类型（对应 Haskell 的 TInt / TStr / TBool）
 pub enum ColumnType {
     Int,
     Str,
     Bool,
 }
 
-/// 一列的 schema。
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+/// 一列的 schema
 pub struct SchemaColumn {
     pub name: String,
     pub ty: ColumnType,
 }
 
-/// 请求；method 字段做 tag。
 #[derive(Debug, Serialize, Deserialize)]
 #[serde(tag = "method", rename_all = "snake_case")]
+/// 请求：method 字段决定类型
 pub enum Request {
     Ping,
     Scan { table: String },
@@ -38,16 +38,25 @@ pub enum Request {
     ReplaceAll { table: String, rows: Vec<Row> },
     ListTables,
     DescribeTable { table: String },
+    CreateTable {
+        table: String,
+        columns: Vec<SchemaColumn>,
+    },
+    DropTable { table: String },
 }
 
-/// 响应；status 字段做 tag。
 #[derive(Debug, Serialize, Deserialize)]
 #[serde(tag = "status", rename_all = "lowercase")]
+/// 响应：status 字段决定类型
 pub enum Response {
     Pong,
     Rows { rows: Vec<Row> },
     Tables { tables: Vec<String> },
-    Schema { columns: Vec<SchemaColumn> },
+    Schema {
+        columns: Vec<SchemaColumn>,
+        #[serde(default)]
+        row_count: u64,
+    },
     Ok,
     Error { message: String },
 }
diff --git a/chusql-storage/src/wal.rs b/chusql-storage/src/wal.rs
index 7dbb141..5f7251e 100644
--- a/chusql-storage/src/wal.rs
+++ b/chusql-storage/src/wal.rs
@@ -1,15 +1,3 @@
-//! 简化版 WAL：写前日志 + 崩溃恢复。
-//!
-//! 条目格式：
-//!   [u32 body_len][body]
-//!   body = [u64 LSN][u8 操作类型][u16 表名长度][表名字节][JSON 载荷]
-//!
-//! 简化版约束：
-//!   - 最多只有一条未完成的操作。写成功就清空 WAL。
-//!   - 不做 checkpoint / redo / undo / 事务。
-//!
-//! 崩溃恢复：
-//!   - 启动时若 WAL 非空，重放那一条，然后清空。
 
 use std::fs::{File, OpenOptions};
 use std::io::{self, Read, Write};
@@ -19,12 +7,13 @@ use serde::{Deserialize, Serialize};
 
 use crate::protocol::Row;
 
-/// 操作类型标记。
+// 预写日志：先记操作并 fsync，再改数据；重启重放残留。
+
 const OP_INSERT: u8 = 1;
 const OP_REPLACE_ALL: u8 = 2;
 
-/// 一条 WAL 操作。
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+/// 一条待写入的操作
 pub enum WalOp {
     Insert {
         table: String,
@@ -37,25 +26,26 @@ pub enum WalOp {
     },
 }
 
-/// WAL 文件句柄。
+/// WAL 文件
 pub struct Wal {
     path: PathBuf,
 }
 
 impl Wal {
-    /// 绑定到 WAL 文件路径；首次 append 时自动创建文件。
+    // 读写
+    /// 绑定 WAL 文件路径
     pub fn new<P: AsRef<Path>>(path: P) -> Self {
         Wal {
             path: path.as_ref().to_path_buf(),
         }
     }
 
-    /// 日志文件路径。
+    /// 日志文件路径
     pub fn path(&self) -> &Path {
         &self.path
     }
 
-    /// 清空 WAL；文件不存在则什么都不做。
+    /// 清空 WAL
     pub fn clear(&self) -> io::Result<()> {
         if self.path.exists() {
             let f = OpenOptions::new().write(true).open(&self.path)?;
@@ -65,7 +55,7 @@ impl Wal {
         Ok(())
     }
 
-    /// 追加一条操作并 fsync。
+    /// 追加一条并 fsync
     pub fn append(&self, op: &WalOp) -> io::Result<()> {
         let bytes = encode(op)?;
         let mut f = OpenOptions::new()
@@ -77,7 +67,7 @@ impl Wal {
         Ok(())
     }
 
-    /// 读取当前 WAL；空文件 / 不存在返回 None。
+    /// 读当前 WAL；空则 None
     pub fn read(&self) -> io::Result<Option<WalOp>> {
         if !self.path.exists() {
             return Ok(None);
@@ -98,9 +88,9 @@ impl Wal {
     }
 }
 
-/// 把一条操作编成字节。
+// 编解码
+/// 把操作编成字节
 fn encode(op: &WalOp) -> io::Result<Vec<u8>> {
-    // 先编出 (类型, 表名, 载荷)
     let (op_type, table, payload) = match op {
         WalOp::Insert { table, row, key } => {
             let p = serde_json::to_vec(&(row, key)).map_err(io::Error::other)?;
@@ -114,8 +104,6 @@ fn encode(op: &WalOp) -> io::Result<Vec<u8>> {
 
     let table_bytes = table.as_bytes();
 
-    // body = [u64 LSN][u8 类型][u16 表名长度][表名][载荷]
-    // 简化版 LSN 固定为 1；完整版会改成真正递增。
     let lsn: u64 = 1;
     let mut body = Vec::with_capacity(8 + 1 + 2 + table_bytes.len() + payload.len());
     body.extend_from_slice(&lsn.to_le_bytes());
@@ -124,32 +112,25 @@ fn encode(op: &WalOp) -> io::Result<Vec<u8>> {
     body.extend_from_slice(table_bytes);
     body.extend_from_slice(&payload);
 
-    // 整条 = [u32 body_len][body]
     let mut out = Vec::with_capacity(4 + body.len());
     out.extend_from_slice(&(body.len() as u32).to_le_bytes());
     out.extend_from_slice(&body);
     Ok(out)
 }
 
-/// 解析一条 WAL 条目。
-///
-/// - `Ok(Some(op))`：成功解析出操作
-/// - `Ok(None)`：尾部被截断（写入一半就断电），按"没有这条"处理
-/// - `Err(_)`：字节流本身损坏，抛错
+/// 从字节解回操作
 fn decode(buf: &[u8]) -> Result<Option<WalOp>, String> {
     if buf.len() < 4 {
         return Ok(None);
     }
     let body_len = u32::from_le_bytes([buf[0], buf[1], buf[2], buf[3]]) as usize;
     if buf.len() < 4 + body_len {
-        // 尾部被截断——忽略
         return Ok(None);
     }
     let body = &buf[4..4 + body_len];
     if body.len() < 8 + 1 + 2 {
         return Err("body too short".into());
     }
-    // LSN 简化版忽略
     let _lsn = u64::from_le_bytes([
         body[0], body[1], body[2], body[3], body[4], body[5], body[6], body[7],
     ]);
diff --git a/chusql-storage/tests/btree_test.rs b/chusql-storage/tests/btree_test.rs
index 998a916..38442f9 100644
--- a/chusql-storage/tests/btree_test.rs
+++ b/chusql-storage/tests/btree_test.rs
@@ -1,10 +1,10 @@
 use chusql_storage::btree::DiskBTree;
 use chusql_storage::config::{DEFAULT_BTREE_ORDER, DEFAULT_PAGE_SIZE};
+use chusql_storage::page::DEFAULT_POOL_SIZE;
 
-// B+ 树测试：空树查询、插入后查找、重开文件数据仍在、覆盖同一个键、升序遍历、
-// 倒序插入 500 个键、页大小 / order 可以配置、配置和文件头对不上时报错。
+// B+ 树测试：插查、重开、分裂、页大小与 order 校验。
 
-/// 空树的 get 返回 None，遍历返回空。
+/// 空树查不到，遍历为空
 #[test]
 fn empty_tree_get() {
     let dir = tempfile::tempdir().unwrap();
@@ -12,13 +12,14 @@ fn empty_tree_get() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
     assert_eq!(t.get(1).unwrap(), None);
     assert_eq!(t.iter_all().unwrap(), vec![]);
 }
 
-/// 插 100 个键，每个都能按 key 查回来。
+/// 插 100 个键都能查回
 #[test]
 fn insert_then_get() {
     let dir = tempfile::tempdir().unwrap();
@@ -26,6 +27,7 @@ fn insert_then_get() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
     for i in 0..100 {
@@ -36,24 +38,24 @@ fn insert_then_get() {
     }
 }
 
-/// 关掉再打开同一个索引文件，数据还在。
+/// 重开文件数据还在
 #[test]
 fn reopen_persists() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.idx");
     {
-        let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER).unwrap();
+        let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).unwrap();
         for i in 0..50 {
             t.insert(i, i as u64).unwrap();
         }
     }
-    let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER).unwrap();
+    let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).unwrap();
     for i in 0..50 {
         assert_eq!(t.get(i).unwrap(), Some(i as u64));
     }
 }
 
-/// 同一个键插两次，后写的值生效。
+/// 同一个键后写的值生效
 #[test]
 fn update_existing() {
     let dir = tempfile::tempdir().unwrap();
@@ -61,6 +63,7 @@ fn update_existing() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
     t.insert(5, 100).unwrap();
@@ -68,7 +71,7 @@ fn update_existing() {
     assert_eq!(t.get(5).unwrap(), Some(200));
 }
 
-/// 倒序插入后遍历，结果仍按 key 升序。
+/// 倒序插入后遍历仍升序
 #[test]
 fn iter_all_sorted() {
     let dir = tempfile::tempdir().unwrap();
@@ -76,6 +79,7 @@ fn iter_all_sorted() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
     for i in (0..50).rev() {
@@ -88,7 +92,7 @@ fn iter_all_sorted() {
     }
 }
 
-/// 倒序插入 500 个键（必然多次分裂），每个键都能查到。
+/// 倒序插 500 个键都能查到
 #[test]
 fn reverse_order_insert() {
     let dir = tempfile::tempdir().unwrap();
@@ -96,6 +100,7 @@ fn reverse_order_insert() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
     for i in (0..500).rev() {
@@ -106,11 +111,11 @@ fn reverse_order_insert() {
     }
 }
 
-/// 页大小和 order 都可以配置：512 字节的页 + 8 个孩子照样能插能查。
+/// 512 字节页 + 8 个孩子可用
 #[test]
 fn custom_page_size_and_order() {
     let dir = tempfile::tempdir().unwrap();
-    let mut t = DiskBTree::open(dir.path().join("t.idx"), 512, 8).unwrap();
+    let mut t = DiskBTree::open(dir.path().join("t.idx"), 512, 8, DEFAULT_POOL_SIZE).unwrap();
     for i in 0..200 {
         t.insert(i, i as u64 + 1).unwrap();
     }
@@ -119,32 +124,32 @@ fn custom_page_size_and_order() {
     }
 }
 
-/// 文件头里记着页大小和 order：换配置再打开要报错，而不是读出乱七八糟的东西。
+/// 页大小或 order 不符要报错
 #[test]
 fn config_mismatch_errors() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.idx");
     {
-        let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER).unwrap();
+        let mut t = DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).unwrap();
         t.insert(1, 1).unwrap();
     }
-    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, 8).is_err());
-    assert!(DiskBTree::open(&path, 8192, DEFAULT_BTREE_ORDER).is_err());
-    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER).is_ok());
+    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, 8, DEFAULT_POOL_SIZE).is_err());
+    assert!(DiskBTree::open(&path, 8192, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).is_err());
+    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).is_ok());
 }
 
-/// 不是本项目的索引文件（比如随便一个空文件）要报错。
+/// 不是索引文件要报错
 #[test]
 fn not_an_index_file_errors() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("junk.idx");
     std::fs::write(&path, vec![7u8; DEFAULT_PAGE_SIZE]).unwrap();
-    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER).is_err());
+    assert!(DiskBTree::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_BTREE_ORDER, DEFAULT_POOL_SIZE).is_err());
 }
 
-/// order 放不进一页时直接拒绝。
+/// order 放不进一页要报错
 #[test]
 fn order_too_large_for_page_errors() {
     let dir = tempfile::tempdir().unwrap();
-    assert!(DiskBTree::open(dir.path().join("t.idx"), 512, 300).is_err());
+    assert!(DiskBTree::open(dir.path().join("t.idx"), 512, 300, DEFAULT_POOL_SIZE).is_err());
 }
diff --git a/chusql-storage/tests/catalog_test.rs b/chusql-storage/tests/catalog_test.rs
index 8faa679..b6fc394 100644
--- a/chusql-storage/tests/catalog_test.rs
+++ b/chusql-storage/tests/catalog_test.rs
@@ -2,6 +2,10 @@ use chusql_storage::catalog::Catalog;
 use chusql_storage::protocol::{ColumnType, Row};
 use serde_json::json;
 
+// 数据字典测试：补列、去重、未知表。
+
+
+
 fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     let mut m = Row::new();
     for (k, v) in pairs {
@@ -10,6 +14,7 @@ fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     m
 }
 
+/// 空文件得到空字典
 #[test]
 fn empty_file_gives_empty_catalog() {
     let dir = tempfile::tempdir().unwrap();
@@ -18,6 +23,7 @@ fn empty_file_gives_empty_catalog() {
     assert_eq!(c.table_names().len(), 0);
 }
 
+/// 补列之后能查到 schema
 #[test]
 fn ensure_then_describe() {
     let dir = tempfile::tempdir().unwrap();
@@ -39,6 +45,7 @@ fn ensure_then_describe() {
     assert_eq!(name_col.ty, ColumnType::Str);
 }
 
+/// 再插入不会重复列
 #[test]
 fn second_insert_does_not_duplicate_columns() {
     let dir = tempfile::tempdir().unwrap();
@@ -50,6 +57,7 @@ fn second_insert_does_not_duplicate_columns() {
     assert_eq!(c.describe("users").unwrap().columns.len(), 1);
 }
 
+/// 未知表返回 None
 #[test]
 fn describe_unknown_returns_none() {
     let dir = tempfile::tempdir().unwrap();
diff --git a/chusql-storage/tests/config_test.rs b/chusql-storage/tests/config_test.rs
index 6c30aa9..457be22 100644
--- a/chusql-storage/tests/config_test.rs
+++ b/chusql-storage/tests/config_test.rs
@@ -6,10 +6,9 @@ use chusql_storage::config::{
 };
 use chusql_storage::log::Level;
 
-// 配置测试：没有文件时全默认、文件里写了才覆盖、环境变量优先于文件、
-// 非法值 / 未知键要报错、每个选项的来源都记得下来。
+// 配置测试：默认值、文件覆盖、环境变量优先、非法值报错。
 
-/// 没有配置文件、没有环境变量：全部走内置默认值。
+/// 无文件时全默认
 #[test]
 fn defaults_without_file() {
     let loaded = config::resolve(None, None, &|_| None).unwrap();
@@ -23,7 +22,7 @@ fn defaults_without_file() {
     assert_eq!(loaded.config.log_level, Level::Info);
 }
 
-/// 文件里只写了一项：这一项生效，其余回退默认（并且来源记得清清楚楚）。
+/// 只覆盖文件里写了的项
 #[test]
 fn file_overrides_only_written_keys() {
     let path = PathBuf::from("t.toml");
@@ -41,15 +40,16 @@ fn file_overrides_only_written_keys() {
     assert_eq!(order.2, Origin::Default);
 }
 
-/// 五项全写：值都生效，来源都是文件。
+/// 六项全写都生效
 #[test]
 fn file_all_keys() {
-    let text = "[page]\nsize = 8192\n[btree]\norder = 32\n[storage]\ndata_dir = \"mydata\"\n[server]\npipe_name = \"mypipe\"\n[log]\nlevel = \"debug\"\n";
+    let text = "[page]\nsize = 8192\n[btree]\norder = 32\n[buffer]\npool_size = 128\n[storage]\ndata_dir = \"mydata\"\n[server]\npipe_name = \"mypipe\"\n[log]\nlevel = \"debug\"\n";
     let path = PathBuf::from("t.toml");
     let loaded = config::resolve(Some(text), Some(path.clone()), &|_| None).unwrap();
 
     assert_eq!(loaded.config.page_size, 8192);
     assert_eq!(loaded.config.btree_order, 32);
+    assert_eq!(loaded.config.pool_size, 128);
     assert_eq!(loaded.config.data_dir, PathBuf::from("mydata"));
     assert_eq!(loaded.config.pipe_name, "mypipe");
     assert_eq!(loaded.config.log_level, Level::Debug);
@@ -61,7 +61,7 @@ fn file_all_keys() {
     );
 }
 
-/// 环境变量优先于文件。
+/// 环境变量优先于文件
 #[test]
 fn env_beats_file() {
     let text = "[storage]\ndata_dir = \"from-file\"\n";
@@ -77,14 +77,14 @@ fn env_beats_file() {
     assert_eq!(dir.2, Origin::Env("CHUSQL_DATA_DIR"));
 }
 
-/// 日志等级写错要报错，而不是悄悄按默认跑。
+/// 日志等级非法要报错
 #[test]
 fn rejects_bad_log_level() {
     let err = config::resolve(Some("[log]\nlevel = \"loud\"\n"), None, &|_| None).unwrap_err();
     assert!(err.contains("log.level"), "got {}", err);
 }
 
-/// 页大小必须是 512..65536 之间的 2 的幂。
+/// 页大小非法要报错
 #[test]
 fn rejects_bad_page_size() {
     let err = config::resolve(Some("[page]\nsize = 3000\n"), None, &|_| None).unwrap_err();
@@ -94,7 +94,7 @@ fn rejects_bad_page_size() {
     assert!(err.contains("page.size"), "got {}", err);
 }
 
-/// order 太小、或者放不进一页，都要报错。
+/// order 非法要报错
 #[test]
 fn rejects_bad_btree_order() {
     let err = config::resolve(Some("[btree]\norder = 2\n"), None, &|_| None).unwrap_err();
@@ -104,14 +104,14 @@ fn rejects_bad_btree_order() {
     assert!(err.contains("does not fit"), "got {}", err);
 }
 
-/// 配置里出现认不出来的键要报错（拼错了不能当没看见）。
+/// 未知配置键要报错
 #[test]
 fn rejects_unknown_key() {
     let err = config::resolve(Some("[page]\nsizes = 4096\n"), None, &|_| None).unwrap_err();
     assert!(err.contains("bad config"), "got {}", err);
 }
 
-/// 环境变量给了非法值也要报错。
+/// 环境变量非法要报错
 #[test]
 fn rejects_bad_env_value() {
     let env = |k: &str| (k == "CHUSQL_PAGE_SIZE").then(|| "big".to_string());
@@ -119,7 +119,7 @@ fn rejects_bad_env_value() {
     assert!(err.contains("CHUSQL_PAGE_SIZE"), "got {}", err);
 }
 
-/// 来源文案要能说清"哪来的"。
+/// 来源文案正确
 #[test]
 fn origin_description() {
     assert_eq!(Origin::Default.describe(), "default");
diff --git a/chusql-storage/tests/heap_test.rs b/chusql-storage/tests/heap_test.rs
index 88348d2..624113b 100644
--- a/chusql-storage/tests/heap_test.rs
+++ b/chusql-storage/tests/heap_test.rs
@@ -1,11 +1,11 @@
 use chusql_storage::config::DEFAULT_PAGE_SIZE;
 use chusql_storage::heap::HeapTable;
+use chusql_storage::page::DEFAULT_POOL_SIZE;
 use chusql_storage::protocol::Row;
 use serde_json::json;
 
-// 堆表测试：插入 + 全表扫描、跨页多行、大行、超大行报错、重开文件后数据还在、自定义页大小。
+// 堆表测试：插查、跨页、大行、重开、索引重建。
 
-/// 造一行测试数据（列名 → JSON 值）。
 fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     let mut m = Row::new();
     for (k, v) in pairs {
@@ -14,12 +14,12 @@ fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     m
 }
 
-/// 插一行再扫描，能原样读回来。
+/// 插一行再扫描读回
 #[test]
 fn insert_and_scan_one_row() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.db");
-    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
 
     t.insert(&row(&[("id", json!(1)), ("name", json!("Alice"))]))
         .unwrap();
@@ -30,12 +30,12 @@ fn insert_and_scan_one_row() {
     assert_eq!(rows[0]["name"], json!("Alice"));
 }
 
-/// 插 500 行（必然跨多页），扫描回来的行数和顺序都要对。
+/// 500 行跨页顺序不变
 #[test]
 fn insert_many_rows_cross_pages() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.db");
-    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
 
     for i in 0..500 {
         t.insert(&row(&[("id", json!(i))])).unwrap();
@@ -43,18 +43,17 @@ fn insert_many_rows_cross_pages() {
 
     let rows = t.scan().unwrap();
     assert_eq!(rows.len(), 500);
-    // 顺序保持
     for (i, r) in rows.iter().enumerate() {
         assert_eq!(r["id"], json!(i as i64));
     }
 }
 
-/// 约 2KB 的大行也要能放进一页。
+/// 2KB 大行放得下
 #[test]
 fn large_row_still_fits() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.db");
-    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
 
     let big = "x".repeat(2000);
     t.insert(&row(&[("data", json!(big.clone()))])).unwrap();
@@ -64,43 +63,43 @@ fn large_row_still_fits() {
     assert_eq!(rows[0]["data"], json!(big));
 }
 
-/// 超过一页容量的行要报错，而不是悄悄写坏。
+/// 超页的行要报错
 #[test]
 fn row_too_large_errors() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.db");
-    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
 
     let huge = "x".repeat(10_000);
     let err = t.insert(&row(&[("data", json!(huge))]));
     assert!(err.is_err());
 }
 
-/// 关掉再重新打开同一个文件，之前插入的数据还在。
+/// 重开文件数据还在
 #[test]
 fn reopen_and_scan() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("t.db");
 
     {
-        let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+        let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
         t.insert(&row(&[("id", json!(1))])).unwrap();
         t.insert(&row(&[("id", json!(2))])).unwrap();
     }
 
-    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let mut t = HeapTable::open(&path, DEFAULT_PAGE_SIZE, DEFAULT_POOL_SIZE).unwrap();
     let rows = t.scan().unwrap();
     assert_eq!(rows.len(), 2);
     assert_eq!(rows[0]["id"], json!(1));
     assert_eq!(rows[1]["id"], json!(2));
 }
 
-/// 页大小可以配置：512 字节的页装得下小行、放不下大行，行数不变。
+/// 512 字节页可用
 #[test]
 fn custom_page_size() {
     let dir = tempfile::tempdir().unwrap();
     let path = dir.path().join("small.db");
-    let mut t = HeapTable::open(&path, 512).unwrap();
+    let mut t = HeapTable::open(&path, 512, DEFAULT_POOL_SIZE).unwrap();
 
     for i in 0..50 {
         t.insert(&row(&[("id", json!(i))])).unwrap();
@@ -111,7 +110,7 @@ fn custom_page_size() {
     assert!(t.insert(&row(&[("data", json!(big))])).is_err());
 }
 
-/// 整表改写之后索引必须跟着重建：旧键查不到，新行按 id 能查到。
+/// 整表改写后索引重建
 #[test]
 fn replace_all_rebuilds_index() {
     let dir = tempfile::tempdir().unwrap();
@@ -120,6 +119,7 @@ fn replace_all_rebuilds_index() {
         dir.path().join("t.idx"),
         DEFAULT_PAGE_SIZE,
         chusql_storage::config::DEFAULT_BTREE_ORDER,
+        DEFAULT_POOL_SIZE,
     )
     .unwrap();
 
diff --git a/chusql-storage/tests/page_test.rs b/chusql-storage/tests/page_test.rs
index 729ba6e..d68a086 100644
--- a/chusql-storage/tests/page_test.rs
+++ b/chusql-storage/tests/page_test.rs
@@ -1,10 +1,9 @@
 use chusql_storage::config::DEFAULT_PAGE_SIZE;
 use chusql_storage::page::{Page, PageFile};
 
-// 页文件测试：一页的读写、页号越界报错、追加页让文件变长、多页互不干扰、覆写同一页、
-// 自定义页大小、页大小和文件对不上时报错。
+// 页文件测试：读写、追加、覆写、页大小校验与页缓存。
 
-/// 写入一页再读回来，内容和长度都应该一致。
+/// 写一页再读回一致
 #[test]
 fn write_then_read_page() {
     let dir = tempfile::tempdir().unwrap();
@@ -23,7 +22,7 @@ fn write_then_read_page() {
     assert_eq!(read.data.len(), DEFAULT_PAGE_SIZE);
 }
 
-/// 空文件读第 0 页应该报错。
+/// 空文件读第 0 页报错
 #[test]
 fn read_out_of_range_returns_error() {
     let dir = tempfile::tempdir().unwrap();
@@ -33,7 +32,7 @@ fn read_out_of_range_returns_error() {
     assert!(pf.read_page(0).is_err());
 }
 
-/// 每 append 一页，num_pages 就加一。
+/// 追加让页数加一
 #[test]
 fn append_grows_file() {
     let dir = tempfile::tempdir().unwrap();
@@ -50,7 +49,7 @@ fn append_grows_file() {
     assert_eq!(pf.num_pages().unwrap(), 3);
 }
 
-/// 页 0 和页 1 的内容互不影响。
+/// 两页内容互不影响
 #[test]
 fn two_pages_independent() {
     let dir = tempfile::tempdir().unwrap();
@@ -69,7 +68,7 @@ fn two_pages_independent() {
     assert_eq!(pf.read_page(1).unwrap().data[0], 2);
 }
 
-/// 覆写同一页：读到的是新内容，页数不变。
+/// 覆写同页读到新内容
 #[test]
 fn overwrite_page() {
     let dir = tempfile::tempdir().unwrap();
@@ -89,25 +88,20 @@ fn overwrite_page() {
     assert_eq!(pf.num_pages().unwrap(), 1);
 }
 
-/// 页大小可以配置：512 字节的页照样读写，文件按 512 字节对齐。
+/// 512 字节页可用
 #[test]
 fn custom_page_size() {
     let dir = tempfile::tempdir().unwrap();
-    let path = dir.path().join("small.db");
-
+    let path = dir.path().join("t.db");
     let mut pf = PageFile::open(&path, 512).unwrap();
-    assert_eq!(pf.page_size(), 512);
 
-    let mut p = Page::new(0, 512);
-    p.data[511] = 9;
-    pf.write_page(&p).unwrap();
+    pf.write_page(&Page::new(0, 512)).unwrap();
+    pf.flush().unwrap();
 
-    assert_eq!(pf.read_page(0).unwrap().data[511], 9);
-    assert_eq!(pf.num_pages().unwrap(), 1);
     assert_eq!(std::fs::metadata(&path).unwrap().len(), 512);
 }
 
-/// 文件长度不是页大小整数倍（比如页大小被改过）要报错，而不是算出错误的页数。
+/// 长度不是整数倍要报错
 #[test]
 fn mismatched_file_length_errors() {
     let dir = tempfile::tempdir().unwrap();
@@ -118,7 +112,7 @@ fn mismatched_file_length_errors() {
     assert!(pf.num_pages().is_err());
 }
 
-/// 页大小对不上的页不许写进去。
+/// 页大小不符拒绝写入
 #[test]
 fn write_wrong_sized_page_errors() {
     let dir = tempfile::tempdir().unwrap();
@@ -127,3 +121,43 @@ fn write_wrong_sized_page_errors() {
     let mut pf = PageFile::open(&path, 512).unwrap();
     assert!(pf.write_page(&Page::new(0, 1024)).is_err());
 }
+
+/// 第二次读命中缓存
+#[test]
+fn cache_hit_avoids_second_read() {
+    let dir = tempfile::tempdir().unwrap();
+    let path = dir.path().join("t.db");
+
+    {
+        let mut pf = PageFile::open(&path, 4096).unwrap();
+        pf.write_page(&Page::new(0, 4096)).unwrap();
+        pf.flush().unwrap();
+    }
+
+    let mut pf = PageFile::open(&path, 4096).unwrap();
+    let _ = pf.read_page(0).unwrap();
+    let _ = pf.read_page(0).unwrap();
+    let _ = pf.read_page(0).unwrap();
+
+    assert_eq!(pf.hits(), 2);
+    assert_eq!(pf.misses(), 1);
+    assert!(pf.hit_rate() > 0.6);
+}
+
+/// 退出时脏页写回
+#[test]
+fn dirty_page_flushed_on_drop() {
+    let dir = tempfile::tempdir().unwrap();
+    let path = dir.path().join("t.db");
+
+    {
+        let mut pf = PageFile::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+        let mut p = Page::new(0, DEFAULT_PAGE_SIZE);
+        p.data[0] = 42;
+        pf.write_page(&p).unwrap();
+    }
+
+    let mut pf2 = PageFile::open(&path, DEFAULT_PAGE_SIZE).unwrap();
+    let p = pf2.read_page(0).unwrap();
+    assert_eq!(p.data[0], 42);
+}
diff --git a/chusql-storage/tests/pipe_test.rs b/chusql-storage/tests/pipe_test.rs
index a65f202..23283ef 100644
--- a/chusql-storage/tests/pipe_test.rs
+++ b/chusql-storage/tests/pipe_test.rs
@@ -9,9 +9,9 @@ use interprocess::local_socket::{
 };
 use interprocess::TryClone;
 
-// 命名管道集成测试：起 server 子进程，用唯一管道名，测试之间互不干扰。
+// 命名管道集成测试：起真 server，跑协议、索引与配置。
 
-/// 生成唯一管道名，避免测试之间抢占。
+/// 唯一管道名，避免测试互抢
 fn unique_pipe_name() -> String {
     let id = std::process::id();
     let ns = std::time::SystemTime::now()
@@ -21,18 +21,18 @@ fn unique_pipe_name() -> String {
     format!("chusql-test-{}-{}", id, ns)
 }
 
-/// 持有 server 子进程，Drop 时杀掉。
+/// 持有 server 子进程，退出时杀掉
 struct ServerProc(Child);
 
 impl Drop for ServerProc {
-    /// 测试结束时杀掉子进程并回收，避免留下孤儿进程。
+    /// 测试结束杀掉子进程
     fn drop(&mut self) {
         let _ = self.0.kill();
         let _ = self.0.wait();
     }
 }
 
-/// 启动 server 子进程，并等管道可连（最多 5 秒）。
+/// 起 server，等管道可连
 fn start_server(pipe: &str) -> (ServerProc, tempfile::TempDir) {
     let data = tempfile::tempdir().unwrap();
 
@@ -57,7 +57,7 @@ fn start_server(pipe: &str) -> (ServerProc, tempfile::TempDir) {
     panic!("server did not start within 5s");
 }
 
-/// 连到指定管道。
+/// 连到指定管道
 fn connect(pipe: &str) -> std::io::Result<LocalSocketStream> {
     let name = pipe
         .to_ns_name::<GenericNamespaced>()
@@ -65,7 +65,7 @@ fn connect(pipe: &str) -> std::io::Result<LocalSocketStream> {
     LocalSocketStream::connect(name)
 }
 
-/// 发一行请求，读一行响应。
+/// 发一行请求读一行响应
 fn send(stream: &mut LocalSocketStream, line: &str) -> String {
     stream.write_all(line.as_bytes()).unwrap();
     stream.write_all(b"\n").unwrap();
@@ -77,7 +77,7 @@ fn send(stream: &mut LocalSocketStream, line: &str) -> String {
     buf.trim().to_string()
 }
 
-/// ping 应该回 pong。
+/// ping 回 pong
 #[test]
 fn ping_pong() {
     let pipe = unique_pipe_name();
@@ -87,7 +87,7 @@ fn ping_pong() {
     assert_eq!(send(&mut c, r#"{"method":"ping"}"#), r#"{"status":"pong"}"#);
 }
 
-/// 插一行再 scan，能扫到刚插进去的数据。
+/// 插入后能扫到
 #[test]
 fn insert_then_scan() {
     let pipe = unique_pipe_name();
@@ -104,6 +104,7 @@ fn insert_then_scan() {
     assert!(r2.contains("Alice"), "scan response: {}", r2);
 }
 
+/// 不存在的表报错
 #[test]
 fn scan_unknown_table_errors() {
     let pipe = unique_pipe_name();
@@ -115,6 +116,7 @@ fn scan_unknown_table_errors() {
     assert!(r.contains("unknown table"), "got {}", r);
 }
 
+/// 列出已建的表
 #[test]
 fn list_tables_returns_created_tables() {
     let pipe = unique_pipe_name();
@@ -129,6 +131,7 @@ fn list_tables_returns_created_tables() {
     assert!(r.contains("orders"), "got {}", r);
 }
 
+/// 整表替换只剩新行
 #[test]
 fn replace_all_replaces_rows() {
     let pipe = unique_pipe_name();
@@ -149,13 +152,13 @@ fn replace_all_replaces_rows() {
     assert!(!r.contains("Alice"), "old row should be gone: {}", r);
 }
 
+/// 带 key 插入后能按下标查
 #[test]
 fn insert_with_key_then_lookup() {
     let pipe = unique_pipe_name();
     let (_srv, _data) = start_server(&pipe);
     let mut c = connect(&pipe).unwrap();
 
-    // 带索引键插三行
     for (id, name) in [(1, "Alice"), (2, "Bob"), (3, "Carol")] {
         let req = format!(
             r#"{{"method":"insert","table":"idx_users","row":{{"id":{},"name":"{}"}},"key":{}}}"#,
@@ -165,15 +168,14 @@ fn insert_with_key_then_lookup() {
         assert!(r.contains(r#""status":"ok""#), "insert: {}", r);
     }
 
-    // 命中
     let r = send(&mut c, r#"{"method":"lookup_by_index","table":"idx_users","key":2}"#);
     assert!(r.contains("Bob"), "lookup: {}", r);
 
-    // 未命中
     let r = send(&mut c, r#"{"method":"lookup_by_index","table":"idx_users","key":99}"#);
     assert!(r.contains(r#""rows":[]"#), "miss: {}", r);
 }
 
+/// 不带 key 不建索引
 #[test]
 fn insert_without_key_does_not_index() {
     let pipe = unique_pipe_name();
@@ -185,12 +187,12 @@ fn insert_without_key_does_not_index() {
     assert!(r.contains(r#""rows":[]"#), "got: {}", r);
 }
 
+/// 重开服务后索引仍在
 #[test]
 fn lookup_survives_reopen() {
     let pipe = unique_pipe_name();
     let data = tempfile::tempdir().unwrap();
 
-    // 第一次：写 3 行带 key
     {
         let exe = env!("CARGO_BIN_EXE_server");
         let child = Command::new(exe)
@@ -213,13 +215,11 @@ fn lookup_survives_reopen() {
             );
             send(&mut c, &req);
         }
-        drop(srv);  // 杀 server
+        drop(srv);
     }
 
-    // 等一下，让文件句柄真正释放
     thread::sleep(Duration::from_millis(200));
 
-    // 第二次：重开 server，从索引查到
     let (_srv, _data) = {
         let child = Command::new(env!("CARGO_BIN_EXE_server"))
             .env("CHUSQL_PIPE", &pipe)
@@ -241,7 +241,7 @@ fn lookup_survives_reopen() {
     assert!(r.contains("Bob"), "persist lookup: {}", r);
 }
 
-/// 配置文件里的管道名和数据目录要真的生效（这里不设 CHUSQL_PIPE / CHUSQL_DATA_DIR）。
+/// 配置文件真的生效
 #[test]
 fn config_file_is_used() {
     let dir = tempfile::tempdir().unwrap();
@@ -249,7 +249,6 @@ fn config_file_is_used() {
     let data_dir = dir.path().join("data");
     let config_path = dir.path().join("chusql-storage.toml");
 
-    // TOML 里写正斜杠，省得转义 Windows 路径
     let text = format!(
         "[server]\npipe_name = \"{}\"\n[storage]\ndata_dir = \"{}\"\n[log]\nlevel = \"debug\"\n",
         pipe,
@@ -276,9 +275,62 @@ fn config_file_is_used() {
     let r = send(&mut c, r#"{"method":"insert","table":"cfg","row":{"id":1}}"#);
     assert!(r.contains(r#""status":"ok""#), "insert: {}", r);
 
-    // 数据真的落在配置文件指的那个目录里
     assert!(
         data_dir.join("cfg.db").exists(),
         "data dir from config file was not used"
     );
 }
+
+/// 建表后能查 schema
+#[test]
+fn create_table_then_describe() {
+    let pipe = unique_pipe_name();
+    let (_srv, _data) = start_server(&pipe);
+    let mut c = connect(&pipe).unwrap();
+
+    let r = send(
+        &mut c,
+        r#"{"method":"create_table","table":"ct_users","columns":[{"name":"id","ty":"int"},{"name":"name","ty":"str"}]}"#,
+    );
+    assert!(r.contains(r#""status":"ok""#), "create: {}", r);
+
+    let r = send(&mut c, r#"{"method":"describe_table","table":"ct_users"}"#);
+    assert!(r.contains("id"), "describe: {}", r);
+    assert!(r.contains("name"), "describe: {}", r);
+    assert!(r.contains(r#""ty":"int""#), "describe: {}", r);
+    assert!(r.contains(r#""ty":"str""#), "describe: {}", r);
+}
+
+/// 重复建表报错
+#[test]
+fn create_table_twice_errors() {
+    let pipe = unique_pipe_name();
+    let (_srv, _data) = start_server(&pipe);
+    let mut c = connect(&pipe).unwrap();
+
+    let req = r#"{"method":"create_table","table":"dup","columns":[{"name":"id","ty":"int"}]}"#;
+    let r1 = send(&mut c, req);
+    assert!(r1.contains(r#""status":"ok""#), "first: {}", r1);
+
+    let r2 = send(&mut c, req);
+    assert!(r2.contains(r#""status":"error""#), "second: {}", r2);
+    assert!(r2.contains("already exists"), "second: {}", r2);
+}
+
+/// 新建空表能扫描
+#[test]
+fn scan_empty_table_after_create() {
+    let pipe = unique_pipe_name();
+    let (_srv, _data) = start_server(&pipe);
+    let mut c = connect(&pipe).unwrap();
+
+    let r = send(
+        &mut c,
+        r#"{"method":"create_table","table":"empty_t","columns":[{"name":"id","ty":"int"}]}"#,
+    );
+    assert!(r.contains(r#""status":"ok""#), "create: {}", r);
+
+    let r = send(&mut c, r#"{"method":"scan","table":"empty_t"}"#);
+    assert!(r.contains(r#""status":"rows""#), "scan: {}", r);
+    assert!(r.contains(r#""rows":[]"#), "scan: {}", r);
+}
diff --git a/chusql-storage/tests/wal_test.rs b/chusql-storage/tests/wal_test.rs
index aa55a0a..d0feeb2 100644
--- a/chusql-storage/tests/wal_test.rs
+++ b/chusql-storage/tests/wal_test.rs
@@ -2,6 +2,9 @@ use chusql_storage::protocol::Row;
 use chusql_storage::wal::{Wal, WalOp};
 use serde_json::json;
 
+// WAL 测试：追加、读取、清空、截断尾巴。
+
+
 fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     let mut m = Row::new();
     for (k, v) in pairs {
@@ -10,6 +13,7 @@ fn row(pairs: &[(&str, serde_json::Value)]) -> Row {
     m
 }
 
+/// 写读 Insert 操作
 #[test]
 fn append_and_read_insert() {
     let dir = tempfile::tempdir().unwrap();
@@ -26,6 +30,7 @@ fn append_and_read_insert() {
     assert_eq!(back, op);
 }
 
+/// 写读 ReplaceAll 操作
 #[test]
 fn append_and_read_replace_all() {
     let dir = tempfile::tempdir().unwrap();
@@ -44,6 +49,7 @@ fn append_and_read_replace_all() {
     assert_eq!(back, op);
 }
 
+/// 文件不存在返回 None
 #[test]
 fn missing_file_returns_none() {
     let dir = tempfile::tempdir().unwrap();
@@ -51,6 +57,7 @@ fn missing_file_returns_none() {
     assert!(wal.read().unwrap().is_none());
 }
 
+/// 空文件返回 None
 #[test]
 fn empty_file_returns_none() {
     let dir = tempfile::tempdir().unwrap();
@@ -60,6 +67,7 @@ fn empty_file_returns_none() {
     assert!(wal.read().unwrap().is_none());
 }
 
+/// 清空后读不到
 #[test]
 fn clear_truncates() {
     let dir = tempfile::tempdir().unwrap();
@@ -79,6 +87,7 @@ fn clear_truncates() {
     assert_eq!(std::fs::metadata(&path).unwrap().len(), 0);
 }
 
+/// 尾巴截断被忽略
 #[test]
 fn truncated_tail_is_ignored() {
     let dir = tempfile::tempdir().unwrap();
@@ -92,19 +101,15 @@ fn truncated_tail_is_ignored() {
     })
     .unwrap();
 
-    // 砍掉最后 5 个字节，模拟"写一半断电"
     let full = std::fs::read(&path).unwrap();
     std::fs::write(&path, &full[..full.len() - 5]).unwrap();
 
-    // 读回来应该当作"没有这条"
     assert!(wal.read().unwrap().is_none());
 }
 
+/// 第二次追加会覆盖
 #[test]
 fn overwrite_on_second_append_is_visible() {
-    // 简化版一次只允许一条，append 两次会叠在文件里——
-    // 但正常路径下 clear 先跑，所以实际不会叠加。
-    // 这个测试只验证 read 能解析最前面那一条。
     let dir = tempfile::tempdir().unwrap();
     let wal = Wal::new(dir.path().join("wal.log"));