diff --git a/AGENTS.md b/AGENTS.md
index 42bd2bb..bc0aee8 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -28,5 +28,5 @@
 - 改动说明只在交流中记录。
 
 ## 当前重点
-- 主线已完成：高级优化器 → 并行查询 → M1 会话隔离 → M2 快照事务 → M3 WAL 与崩溃恢复 → M4 表结构进 WAL → M5 系统表统一命名 → M6 检查点按 LSN 部分截断 → M7 事务写写冲突检测 → M8 事务保存点 → M9 角色继承 → M10 转授权。
+- 主线已完成：高级优化器 → 并行查询 → M1 会话隔离 → M2 快照事务 → M3 WAL 与崩溃恢复 → M4 表结构进 WAL → M5 系统表统一命名 → M6 检查点按 LSN 部分截断 → M7 事务写写冲突检测 → M8 事务保存点 → M9 角色继承 → M10 转授权 → M11 FROM 派生表与投影别名。
 - 进度与计数见 `agent_credientials/project-plan.txt`，限制与风险见 `agent_credientials/known-issues.txt`。
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Eval.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Eval.hs
index 752c56a..f2e25df 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Eval.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Eval.hs
@@ -409,6 +409,9 @@ evalRelOpIn db outer (Sort spec op) = do
 evalRelOpIn db outer (Limit n op) = do
     rows <- evalRelOpIn db outer op
     pure (fmap (take n) rows)
+evalRelOpIn db outer (Derived mAlias op) = do
+    rows <- evalRelOpIn db outer op
+    pure (fmap (prefixRows mAlias) rows)
 evalRelOpIn db outer (Join kind l r c) = do
     lres <- evalRelOpIn db outer l
     case lres of
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/JoinOrder.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/JoinOrder.hs
index 47953b5..12cf83a 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/JoinOrder.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/JoinOrder.hs
@@ -21,6 +21,7 @@ pass db _ (Aggregate keys aggs x) = Aggregate keys aggs (pass db False x)
 pass db free (Project cols x) = Project cols (pass db free x)
 pass db free (Compute items x) = Compute items (pass db free x)
 pass db free (Filter p x) = Filter p (pass db free x)
+pass db free (Derived a x) = Derived a (pass db free x)
 pass db free (Join kind l r c)
     | free
     , Just (leaves, conds) <- innerChain (Join kind l r c)
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Op.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Op.hs
index d22cd20..c94da03 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Op.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Op.hs
@@ -17,6 +17,7 @@ data RelOp
     | Sort [(String, SortDir)] RelOp
     | Limit Int RelOp
     | Join JoinKind RelOp RelOp Expr
+    | Derived (Maybe String) RelOp
     deriving (Show, Eq)
 
 -- | 算子会产出哪些列
@@ -39,6 +40,7 @@ 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
+relOpCols db (Derived mAlias x) = map (qualify mAlias) (relOpCols db x)
 
 -- | 连接的显示名
 kindLabel :: JoinKind -> String
@@ -69,5 +71,6 @@ renderPlan = go 0
         Sort s x -> pad ++ "Sort " ++ show s ++ "\n" ++ go (ind + 1) x
         Limit n x -> pad ++ "Limit " ++ show n ++ "\n" ++ go (ind + 1) x
         Join k l r c -> pad ++ kindLabel k ++ " on " ++ show c ++ "\n" ++ go (ind + 1) l ++ "\n" ++ go (ind + 1) r
+        Derived a x -> pad ++ "Derived " ++ show a ++ "\n" ++ go (ind + 1) x
       where
         pad = replicate (ind * 2) ' '
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Optimize.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Optimize.hs
index 1ae7fee..cbebc54 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Optimize.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Optimize.hs
@@ -79,6 +79,7 @@ planHasDivision (Compute items x) = any (hasDivision . snd) items || planHasDivi
 planHasDivision (Project _ x) = planHasDivision x
 planHasDivision (Sort _ x) = planHasDivision x
 planHasDivision (Limit _ x) = planHasDivision x
+planHasDivision (Derived _ x) = planHasDivision x
 planHasDivision _ = False
 
 -- | 是否要全部列
@@ -117,6 +118,7 @@ pushProject db need leaf@(Scan a t _)
     | needsAll need = leaf
     | all (`elem` need) (relOpCols db leaf) = leaf
     | otherwise = Scan a t (Just (nub (map (unqualify a) need)))
+pushProject _ _ (Derived a x) = Derived a x
 pushProject db need leaf@(Lookup _ _ _ _) = pushProjectLeaf db need leaf
 pushProject db need leaf@(Range _ _ _ _ _) = pushProjectLeaf db need leaf
 
@@ -202,6 +204,7 @@ optimizeRelOp db = rewriteNode db . descend
     descend (Sort spec x) = Sort spec (optimizeRelOp db x)
     descend (Limit n x) = Limit n (optimizeRelOp db x)
     descend (Join kind l r c) = Join kind (optimizeRelOp db l) (optimizeRelOp db r) c
+    descend (Derived a x) = Derived a (optimizeRelOp db x)
     descend x = x
 
 -- | 反复跑到不动点
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Planner.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Planner.hs
index 0777bd3..f707e68 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Planner.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Algebra/Planner.hs
@@ -6,18 +6,19 @@ import ChuSQL.Core.Engine.Syntax.AST
 
 -- 计划生成：把语句翻译成算子树。
 
--- | 把 FROM 子句翻成 Scan / Join
-fromToRelOp :: FromClause -> RelOp
-fromToRelOp FromUnit = Unit
-fromToRelOp (FromTable mAlias tbl) = Scan mAlias tbl Nothing
-fromToRelOp (FromJoin kind left mAlias tbl cond) =
-    Join kind (fromToRelOp left) (Scan mAlias tbl Nothing) cond
+-- | FROM 子句翻成关系算子
+fromToRelOp :: FromClause -> Either String RelOp
+fromToRelOp FromUnit = Right Unit
+fromToRelOp (FromTable mAlias tbl) = Right (Scan mAlias tbl Nothing)
+fromToRelOp (FromSubquery mAlias stmt) = Derived mAlias <$> translate stmt
+fromToRelOp (FromJoin kind left right cond) =
+    Join kind <$> fromToRelOp left <*> fromToRelOp right <*> pure cond
 
 -- | 带上 WHERE 的来源
-source :: FromClause -> Maybe Expr -> RelOp
-source fromC mWhere = case mWhere of
-    Nothing -> fromToRelOp fromC
-    Just w -> Filter w (fromToRelOp fromC)
+source :: FromClause -> Maybe Expr -> Either String RelOp
+source fromC mWhere = do
+    op <- fromToRelOp fromC
+    Right (maybe op (`Filter` op) mWhere)
 
 -- | 给用到的聚合起内部列名，同一个聚合只算一次
 nameAggs :: [(String, Expr)] -> [(String, Expr)]
@@ -80,9 +81,11 @@ translate q = case q of
         , selectOrderBy = orderBy
         , selectLimit = mLimit
         } -> do
-            let (plan, _) = grouped groupBy [] (source fromC mWhere)
+            plan0 <- source fromC mWhere
+            let (plan, _) = grouped groupBy [] plan0
             Right (Project cols (limited orderBy mLimit plan))
     SelectExpr items fromC mWhere groupBy orderBy mLimit -> do
-        let (plan, items') = grouped groupBy items (source fromC mWhere)
+        plan0 <- source fromC mWhere
+        let (plan, items') = grouped groupBy items plan0
         Right (Compute items' (limited orderBy mLimit plan))
     _ -> Left "only SELECT is supported by translate"
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Semantic.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Semantic.hs
index 6f6d6ca..88bcbc4 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Semantic.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Semantic.hs
@@ -44,13 +44,21 @@ checkFrom _ _ FromUnit = Right []
 checkFrom db _ (FromTable mAlias tbl) = do
     (key, t) <- resolveTable db tbl
     Right (prefixColumns (Just (deriveQualifier mAlias key)) (tableCols t))
-checkFrom db outer (FromJoin _ left mAlias tbl cond) = do
+checkFrom db _ (FromSubquery mAlias stmt) = do
+    out <- inferSubqueryOutput db (Scope [] []) (Subquery stmt [])
+    Right (prefixColumns mAlias [(name, plainColumn (derivedType t)) | (name, t) <- out])
+checkFrom db outer (FromJoin _ left right cond) = do
     lcols <- checkFrom db outer left
-    (key, t) <- resolveTable db tbl
-    let env = lcols ++ prefixColumns (Just (deriveQualifier mAlias key)) (tableCols t)
+    rcols <- checkFrom db outer right
+    let env = lcols ++ rcols
     checkBool db "ON" (Scope env outer) cond
     Right env
 
+-- | 派生表里 NULL 字面量列没有具体类型，按字符串处理
+derivedType :: InferredType -> ColumnType
+derivedType (InferType t) = t
+derivedType InferNull = CStr
+
 -- | 合并两层列，本层优先且不重复
 scopedEnv :: [(String, Column)] -> [(String, Column)] -> [(String, Column)]
 scopedEnv env outer = env ++ [o | o <- outer, o `notElem` env]
@@ -638,7 +646,8 @@ statementColumns stmt = case stmt of
     -- | 取 FROM 里出现的列
     fromColumns FromUnit = []
     fromColumns (FromTable _ _) = []
-    fromColumns (FromJoin _ l _ _ c) = fromColumns l ++ colsInExpr c
+    fromColumns (FromSubquery _ _) = []
+    fromColumns (FromJoin _ l r c) = fromColumns l ++ fromColumns r ++ colsInExpr c
 
 -- | 取语句的 FROM 子句，没有就是 FromUnit
 statementFrom :: Statement -> FromClause
@@ -692,17 +701,18 @@ resolveSelect _ q = Right q
 -- | 解析投影、条件、排序与连接引用
 resolveQuery :: Database -> [(String, Column)] -> Statement -> [(String, Expr)] -> Either String Statement
 resolveQuery db outer q items = do
-    env <- checkFrom db outer (selectFrom q)
+    source <- resolveSource db outer (selectFrom q)
+    env <- checkFrom db outer source
     -- | 单表无别名时把裸列名换成物理列名；带别名时表头保留别名限定名
     let physical c = case selectFrom q of
             FromTable Nothing tbl -> unqualify (Just (deriveQualifier Nothing tbl)) c
             _ -> c
         -- | 查一列并换算成物理名
         name place c = physical . fst <$> scopedColumnAt place env outer c
-        -- | 换算一个投影项
-        output (_, Col c) = do
+        -- | 换算一个投影项：带别名时保留别名做输出列名
+        output (label, Col c) = do
             k <- name "SELECT" c
-            pure (k, Col k)
+            pure (if label == c then (k, Col k) else (label, Col k))
         output (label, e) = do
             e' <- resolveExpr db env outer (name "SELECT") e
             pure (label, e')
@@ -714,24 +724,68 @@ resolveQuery db outer q items = do
     condition <- mapM (resolveExpr db env outer (name "WHERE")) (selectWhere q)
     grouping <- mapM (name "GROUP BY") (selectGroupBy q)
     ordering <- mapM (\(c, d) -> (\k -> (k, d)) <$> name "ORDER BY" c) (selectOrderBy q)
-    source <- case selectFrom q of
-        FromTable mAlias tbl -> do
-            (key, _) <- resolveTable db tbl
-            Right (FromTable mAlias key)
-        other -> resolveFrom db outer other
     pure $ case q of
         Select{} -> Select (map fst projected) source condition grouping ordering (selectLimit q)
         _ -> SelectExpr projected source condition grouping ordering (selectLimit q)
 
--- | 连接两侧取表名末段作别名；ON 可引用外层列
+-- | 单表不加限定名，其余来源交给 resolveFrom
+resolveSource :: Database -> [(String, Column)] -> FromClause -> Either String FromClause
+resolveSource db outer fromC = case fromC of
+    FromTable mAlias tbl -> do
+        (key, _) <- resolveTable db tbl
+        Right (FromTable mAlias key)
+    other -> resolveFrom db outer other
+
+-- | 连接两侧与派生表都要先解析，再取环境解析 ON
 resolveFrom :: Database -> [(String, Column)] -> FromClause -> Either String FromClause
 resolveFrom _ _ FromUnit = Right FromUnit
 resolveFrom db _ (FromTable alias tbl) = do
     (key, _) <- resolveTable db tbl
     Right (FromTable (Just (deriveQualifier alias key)) key)
-resolveFrom db outer fromC@(FromJoin kind left alias tbl cond) = do
-    env <- checkFrom db outer fromC
+resolveFrom db _ (FromSubquery mAlias stmt) = do
+    inner <- resolveSubqueryStatement db [] stmt
+    named <- nameDerivedColumns inner
+    Right (FromSubquery mAlias named)
+resolveFrom db outer fromC@(FromJoin kind left right cond) = do
     l <- resolveFrom db outer left
-    (key, _) <- resolveTable db tbl
+    r <- resolveFrom db outer right
+    env <- checkFrom db outer (FromJoin kind l r cond)
     c <- resolveExpr db env outer (fmap fst . columnAt "ON" env) cond
-    pure (FromJoin kind l (Just (deriveQualifier alias key)) key c)
+    pure (FromJoin kind l r c)
+
+-- | 派生表的输出列名：列取裸名，表达式保留原标签
+nameDerivedColumns :: Statement -> Either String Statement
+nameDerivedColumns q@Select { selectCols = cols, selectFrom = fromC } = do
+    let names = map lastTablePart cols
+    checkDerivedNames names
+    Right
+        ( SelectExpr
+            [(n, Col c) | (n, c) <- zip names cols]
+            fromC
+            (selectWhere q)
+            (selectGroupBy q)
+            (selectOrderBy q)
+            (selectLimit q)
+        )
+nameDerivedColumns q@SelectExpr { selectItems = items } = do
+    let names = map derivedItemName items
+    checkDerivedNames names
+    Right q { selectItems = zip names (map snd items) }
+nameDerivedColumns _ = Left "FROM: subquery must be a SELECT"
+
+-- | 派生表里一个投影项的输出名：没写别名的列取裸名
+derivedItemName :: (String, Expr) -> String
+derivedItemName (label, Col c)
+    | label == c = lastTablePart c
+    | otherwise = label
+derivedItemName (label, _) = label
+
+-- | 派生表列名不能重复
+checkDerivedNames :: [String] -> Either String ()
+checkDerivedNames = go []
+  where
+    -- | 逐个查有没有见过
+    go _ [] = Right ()
+    go seen (n : ns)
+        | n `elem` seen = Left ("FROM: duplicate column name in subquery: " ++ n)
+        | otherwise = go (n : seen) ns
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/AST.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/AST.hs
index 20da5cf..048edeb 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/AST.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/AST.hs
@@ -73,10 +73,11 @@ data JoinKind
     | LeftJoin
     deriving (Show, Eq)
 
--- | 数据来源：单表、带连接的来源，或空
+-- | 数据来源：单表、派生表（子查询，输出列已改成裸列名）、带连接的来源，或空
 data FromClause
     = FromTable (Maybe String) String
-    | FromJoin JoinKind FromClause (Maybe String) String Expr
+    | FromSubquery (Maybe String) Statement
+    | FromJoin JoinKind FromClause FromClause Expr
     | FromUnit
     deriving (Show, Eq)
 
diff --git a/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/Parser.hs b/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/Parser.hs
index c58a54e..ddf2693 100644
--- a/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/Parser.hs
+++ b/chusql-core/engine/src/ChuSQL/Core/Engine/Syntax/Parser.hs
@@ -300,21 +300,34 @@ joinKind =
         <|> try (keyword "inner" *> keyword "join" *> return InnerJoin)
         <|> (keyword "join" *> return InnerJoin)
 
+-- | FROM 里的一个来源：表或派生表
+fromSource :: Parser FromClause
+fromSource = fromSubquerySource <|> (uncurry FromTable <$> tableRef)
+
+-- | 派生表：括号里的一条 SELECT，必须有别名
+fromSubquerySource :: Parser FromClause
+fromSubquerySource = do
+    stmt <- between (symbol "(") (symbol ")") selectStatement
+    mAlias <- optional ((keyword "as" *> aliasName) <|> aliasName)
+    case mAlias of
+        Nothing -> fail "FROM subquery needs an alias"
+        Just name -> return (FromSubquery (Just name) stmt)
+
 -- | 一个 JOIN ... ON
-joinClause :: Parser (JoinKind, Maybe String, String, Expr)
+joinClause :: Parser (JoinKind, FromClause, Expr)
 joinClause = do
     kind <- joinKind
-    (mAlias, tbl) <- tableRef
+    src <- fromSource
     keyword "on"
     cond <- expr
-    return (kind, mAlias, tbl, cond)
+    return (kind, src, cond)
 
 -- | FROM 子句（可含多个 JOIN）
 fromClause :: Parser FromClause
 fromClause = do
-    (mAlias, tbl) <- tableRef
+    src <- fromSource
     joins <- many joinClause
-    return (foldl (\acc (k, a, t, c) -> FromJoin k acc a t c) (FromTable mAlias tbl) joins)
+    return (foldl (\acc (k, s, c) -> FromJoin k acc s c) src joins)
 
 -- | SELECT 的列清单
 selectList :: Parser [(String, Expr)]
@@ -324,11 +337,17 @@ selectList =
         , sepBy1 selectItem (symbol ",")
         ]
 
--- | 投影标签保留表达式原文
+-- | 投影项：列名或表达式，可带 AS 别名
 selectItem :: Parser (String, Expr)
 selectItem = do
     (source, e) <- match expr
-    pure (case e of Col c -> (c, e); _ -> (reverse (dropWhile isSpace (reverse source)), e))
+    mAlias <- optional (try (keyword "as" *> aliasName))
+    pure (fromMaybe (selectItemLabel source e) mAlias, e)
+
+-- | 投影项的默认标签：列用列名，表达式用原文
+selectItemLabel :: String -> Expr -> String
+selectItemLabel _ (Col c) = c
+selectItemLabel source _ = reverse (dropWhile isSpace (reverse source))
 
 -- | 读 CREATE TABLE
 createTableStatement :: Parser Statement
diff --git a/chusql-core/engine/test/Spec.hs b/chusql-core/engine/test/Spec.hs
index 8be38fb..275238d 100644
--- a/chusql-core/engine/test/Spec.hs
+++ b/chusql-core/engine/test/Spec.hs
@@ -324,8 +324,7 @@ main = hspec $ do
                             FromJoin
                                 InnerJoin
                                 (FromTable Nothing "users")
-                                Nothing
-                                "orders"
+                                (FromTable Nothing "orders")
                                 (Eq (Col "id") (Col "user_id"))
                         , selectWhere = Nothing
                         , selectGroupBy = []
@@ -343,8 +342,7 @@ main = hspec $ do
                             FromJoin
                                 InnerJoin
                                 (FromTable (Just "u") "users")
-                                (Just "o")
-                                "orders"
+                                (FromTable (Just "o") "orders")
                                 (Eq (Col "u.id") (Col "o.user_id"))
                         , selectWhere = Nothing
                         , selectGroupBy = []
@@ -362,8 +360,7 @@ main = hspec $ do
                             FromJoin
                                 LeftJoin
                                 (FromTable (Just "u") "users")
-                                (Just "o")
-                                "orders"
+                                (FromTable (Just "o") "orders")
                                 (Eq (Col "u.id") (Col "o.user_id"))
                         , selectWhere = Nothing
                         , selectGroupBy = []
@@ -378,11 +375,90 @@ main = hspec $ do
                     ( FromJoin
                         LeftJoin
                         (FromTable (Just "u") "users")
-                        (Just "o")
-                        "orders"
+                        (FromTable (Just "o") "orders")
                         (Eq (Col "u.id") (Col "o.user_id"))
                     )
 
+    describe "ChuSQL.Core.Engine (派生表)" $ do
+        -- sql：在默认库上跑 SQL 取结果行
+        let sql input = parseStatement input >>= rowsOf . runStatement testDB
+            -- values：只取结果里的值
+            values input = fmap (map (map snd)) (sql input)
+        it "parses a derived table with an alias" $ do
+            parseStatement "SELECT d.name FROM (SELECT name FROM users) d"
+                `shouldBe` Right
+                    ( Select
+                        { selectCols = ["d.name"]
+                        , selectFrom =
+                            FromSubquery
+                                (Just "d")
+                                (Select ["name"] (FromTable Nothing "users") Nothing [] [] Nothing)
+                        , selectWhere = Nothing
+                        , selectGroupBy = []
+                        , selectOrderBy = []
+                        , selectLimit = Nothing
+                        }
+                    )
+
+        it "requires an alias for a derived table" $ do
+            parseStatement "SELECT name FROM (SELECT name FROM users)" `shouldSatisfy` isLeft
+
+        it "parses a derived table on the right of a JOIN" $ do
+            fmap selectFrom (parseStatement "SELECT d.name FROM users u JOIN (SELECT name FROM users) d ON u.name = d.name")
+                `shouldBe` Right
+                    ( FromJoin
+                        InnerJoin
+                        (FromTable (Just "u") "users")
+                        (FromSubquery (Just "d") (Select ["name"] (FromTable Nothing "users") Nothing [] [] Nothing))
+                        (Eq (Col "u.name") (Col "d.name"))
+                    )
+
+        it "parses a projection alias" $ do
+            parseStatement "SELECT count(*) AS total FROM orders"
+                `shouldBe` Right
+                    ( SelectExpr
+                        [("total", CountAll)]
+                        (FromTable Nothing "orders")
+                        Nothing
+                        []
+                        []
+                        Nothing
+                    )
+
+        it "runs a derived table as a source" $ do
+            values "SELECT d.name FROM (SELECT name FROM users) d"
+                `shouldBe` Right [[VStr "Alice"], [VStr "Bob"], [VStr "Carol"]]
+
+        it "expands the star of a derived table" $ do
+            sql "SELECT * FROM (SELECT id, name FROM users) d"
+                `shouldBe` Right
+                    [ [("d.id", VInt 1), ("d.name", VStr "Alice")]
+                    , [("d.id", VInt 2), ("d.name", VStr "Bob")]
+                    , [("d.id", VInt 3), ("d.name", VStr "Carol")]
+                    ]
+
+        it "joins a derived table with a table" $ do
+            values "SELECT o.id FROM (SELECT id FROM users WHERE age > 20) d JOIN orders o ON o.user_id = d.id ORDER BY o.id"
+                `shouldBe` Right [[VInt 1], [VInt 3]]
+
+        it "runs an aggregate inside a derived table" $ do
+            values "SELECT d.total FROM (SELECT user_id, count(*) AS total FROM orders GROUP BY user_id) d ORDER BY d.total"
+                `shouldBe` Right [[VInt 1], [VInt 2]]
+
+        it "runs a derived table inside a derived table" $ do
+            values "SELECT inner_d.name FROM (SELECT d.name FROM (SELECT name FROM users) d WHERE d.name = 'Bob') inner_d"
+                `shouldBe` Right [[VStr "Bob"]]
+
+        it "keeps a projection alias outside a derived table" $ do
+            sql "SELECT count(*) AS total FROM orders" `shouldBe` Right [[("total", VInt 3)]]
+
+        it "rejects duplicate column names in a derived table" $ do
+            sql "SELECT d.name FROM (SELECT name, name FROM users) d" `shouldSatisfy` isLeft
+
+        it "does not let a derived table see outer columns" $ do
+            sql "SELECT d.name FROM users u JOIN (SELECT name FROM users WHERE id = u.id) d ON u.name = d.name"
+                `shouldSatisfy` isLeft
+
     describe "ChuSQL.Core.Engine (SELECT)" $ do
         -- sql：在默认库上跑 SQL 取结果行
         let sql input = parseStatement input >>= rowsOf . runStatement testDB
@@ -991,8 +1067,7 @@ main = hspec $ do
                         FromJoin
                             InnerJoin
                             (FromTable (Just "u") "users")
-                            (Just "x")
-                            "nonexistent"
+                            (FromTable (Just "x") "nonexistent")
                             (Eq (Col "u.id") (Col "x.id"))
                     , selectWhere = Nothing
                     , selectGroupBy = []
diff --git a/chusql-server/src/ChuSQL/Server/Backend.hs b/chusql-server/src/ChuSQL/Server/Backend.hs
index a8aa8df..f018fb7 100644
--- a/chusql-server/src/ChuSQL/Server/Backend.hs
+++ b/chusql-server/src/ChuSQL/Server/Backend.hs
@@ -283,7 +283,8 @@ statementNeedsDatabase stmt = any (not . T.any (== '.')) (statementTables stmt)
 tableRefsOf :: FromClause -> [Text]
 tableRefsOf FromUnit = []
 tableRefsOf (FromTable _ name) = [T.pack name]
-tableRefsOf (FromJoin _ left _ name cond) = tableRefsOf left ++ [T.pack name] ++ exprTables cond
+tableRefsOf (FromSubquery _ stmt) = statementTables stmt
+tableRefsOf (FromJoin _ left right cond) = tableRefsOf left ++ tableRefsOf right ++ exprTables cond
 
 -- | 表达式里出现的表（子查询是唯一的来路）
 exprTables :: Expr -> [Text]
diff --git a/chusql-server/test/Spec.hs b/chusql-server/test/Spec.hs
index fddc648..fa69888 100644
--- a/chusql-server/test/Spec.hs
+++ b/chusql-server/test/Spec.hs
@@ -643,6 +643,15 @@ privilegeSpec = describe "server privileges" $ do
             Left err -> expectationFailure err
             Right stmt -> authorize service root testDatabase stmt `shouldReturn` Right ()
 
+    it "requires the privilege on the table inside a derived table" $ withPrivileges $ \service root -> do
+        _ <- runPrivilegeCommand service root testDatabase (CreateRoleCommand "reader")
+        _ <- runPrivilegeCommand service root testDatabase (GrantPrivilegesCommand ["select"] "users" "reader" False)
+        _ <- runPrivilegeCommand service root testDatabase (GrantRoleCommand "reader" ["alice"])
+        authorizeSql service (Ordinary testAccount) "SELECT d.name FROM (SELECT name FROM users) d"
+            `shouldReturn` Right ()
+        authorizeSql service (Ordinary testAccount) "SELECT d.name FROM (SELECT product FROM orders) d"
+            `shouldReturn` Left (PrivilegeError "forbidden" "permission denied: SELECT ON orders")
+
     it "keeps the role tables on the real storage" $ withIpcStorage $ do
         base <- ipcBackend
         service <- newPrivileges base
diff --git a/docs/architecture.md b/docs/architecture.md
index a9db245..93b8d2c 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -47,12 +47,12 @@ chusql-server
 
 每条连接拥有独立会话状态，例如当前数据库选择不会影响其他连接。不同连接可以同时执行语句：读请求之间可以并行，写请求之间由存储层排队。
 
-语句里的库前缀和表限定符由引擎在语义层解析：存储层只接受精确的表名键，因此 `FROM sales.orders` 与选定 `sales` 后的 `FROM orders` 指向同一张表。
+语句里的库前缀和表限定符由引擎在语义层解析：存储层只接受精确的表名键，因此 `FROM sales.orders` 与选定 `sales` 后的 `FROM orders` 指向同一张表。FROM 的来源是一棵树：单表、派生表（括号里的子查询，必须带别名）与连接共用同一个 `FromClause`，所以 `JOIN` 两侧都能是派生表。解析派生表时先把内层语句在空作用域里解析成一张“表”——内层不能引用外层列，输出列统一改成裸列名（内层 `u.id` 在外层用 `d.id` 引用），重名直接报错；执行侧对应一个 `Derived` 算子，把内层计划的结果按别名加前缀。派生表不参与连接顺序重排（叶子的行数未知），投影也不下推进去，但内层计划照常做谓词下推与索引改写。投影项的 `AS` 别名与 `SELECT` 的输出列名一起在语义层解析，派生表与最外层查询都按别名暴露列名。
 
 显式事务在会话层实现：`BEGIN` 把当前数据库整库读成内存快照，事务内的语句都在快照上执行；`SAVEPOINT` 把当前快照压进会话里的保存点栈，`ROLLBACK TO` 退回该点并保留它，`RELEASE` 丢掉该点与其后的保存点；`COMMIT` 先把快照、基线与库里现值按行 `id` 逐键比对，检测到写写冲突就报 `serialization_failure` 并保留事务；没有冲突才把差分用一条 `apply_transaction` 请求交给存储层应用；`ROLLBACK` 直接丢弃快照。因此隔离级别是快照读加原子提交：事务里看不到别的事务未提交或后来提交的改动，提交对外一次性可见，冲突由调用方回滚或重试。
 
 WAL 负责崩溃恢复：每条记录带自增 LSN，一组写操作与一条提交标记一次落盘；每组提交在数据和字典都刷盘之后把 `wal.checkpoint` 推进到这条提交的 LSN，含义是「到此为止的改动都已落盘」，再按这个边界丢掉日志前缀——所以日志里通常只有当组在飞的记录。进程重启时只重放检查点之后的记录，按标记分组取已提交的组、丢弃没有标记的整组，重放前逐条做幂等检查作为第二道保险，结束后再把检查点推到最后一条提交。LSN 从检查点与文件尾里较大的那个续号，跨重启单调，`SystemStatus` 应答里的 `last_lsn` 报告该检查点 LSN。建表、删表、建索引、删索引与数据改动走同一条 WAL，恢复时一并重放。
 
-系统数据库及部分管理操作仅允许管理员访问。系统表统一用 `__system_` 前缀：账号表 `__system_users` 对语句通道隐藏，角色、授权、成员三张表（`__system_roles` / `__system_grants` / `__system_members`）只在 `system` 库里可见，权限服务自身也通过 SQL 读写它们；存储启动时把旧名 `sys_roles` / `sys_grants` / `sys_members` 连同数据与索引文件一起迁移过来。角色支持互相继承：`GRANT 角色 A TO 角色 B` 记一条 B 属于 A 的成员关系，判定权限时沿成员关系算出向上闭包再取并集；写入时拒绝成环与自继承，删角色会清掉它两个方向的成员关系。带 `WITH GRANT OPTION` 的授权记在第四张表 `__system_grant_options` 里（同样的角色、权限、对象三列，单独的列存不下就单独一张表，省掉系统表的结构迁移）：普通身份只要手里那条授权带 grant option 就能把同一项权限转授给别的角色，`REVOKE` 仍然只允许管理员，收回授权时连它的 grant option 一起收掉，但不级联收回别人已经转授出去的授权。授权命令由权限服务在会话层之外直接执行，`GRANT` 命令会先按当前库把对象补全成 `库.表` 再落盘，因此判断转授权资格与实际写入用的是同一个对象名。
+系统数据库及部分管理操作仅允许管理员访问。系统表统一用 `__system_` 前缀：账号表 `__system_users` 对语句通道隐藏，角色、授权、带 option 的授权、成员四张表（`__system_roles` / `__system_grants` / `__system_grant_options` / `__system_members`）只在 `system` 库里可见，权限服务自身也通过 SQL 读写它们；存储启动时把旧名 `sys_roles` / `sys_grants` / `sys_members` 连同数据与索引文件一起迁移过来。角色支持互相继承：`GRANT 角色 A TO 角色 B` 记一条 B 属于 A 的成员关系，判定权限时沿成员关系算出向上闭包再取并集；写入时拒绝成环与自继承，删角色会清掉它两个方向的成员关系。带 `WITH GRANT OPTION` 的授权记在第四张表 `__system_grant_options` 里（同样的角色、权限、对象三列，另开一张表省掉给 `__system_grants` 加列带来的系统表结构迁移）：普通身份只要手里那条授权带 grant option 就能把同一项权限转授给别的角色，`REVOKE` 仍然只允许管理员，收回授权时连它的 grant option 一起收掉，但不级联收回别人已经转授出去的授权。授权命令由权限服务在会话层之外直接执行，`GRANT` 命令会先按当前库把对象补全成 `库.表` 再落盘，因此判断转授权资格与实际写入用的是同一个对象名。
 
 服务监听地址、端口和请求限制可在 `chusql.toml` 的 `[server]` 分区中配置。
diff --git a/docs/commands.md b/docs/commands.md
index 331fef3..f61da16 100644
--- a/docs/commands.md
+++ b/docs/commands.md
@@ -45,6 +45,13 @@ csql -f json -e "SELECT count(*) FROM orders"
 - 只有候选唯一时才自动推导前缀；同名的表或列出现在多个候选上会以 `ambiguous table` / `ambiguous column` 报错，需要写全。
 - `FROM orders AS o` 之后只能用 `o.id`，不能再写 `orders.id`。
 
+查询写法：
+
+- `SELECT` 支持 `WHERE`、`ORDER BY`、`LIMIT`、`JOIN` / `LEFT JOIN`、`GROUP BY` 与聚合，以及标量 / `IN` / `EXISTS` 子查询。
+- 来源可以是派生表：`SELECT d.name FROM (SELECT name FROM users) d`。派生表必须带别名，内层不能引用外层列；输出列取裸列名（内层写 `u.id`，外层用 `d.id` 引用）。
+- 投影列可以起别名：`SELECT count(*) AS total FROM orders`，别名就是结果集的列名。`ORDER BY` 仍按来源列解析，要引用派生表的列得写限定名（如 `ORDER BY d.total`）。
+- 鉴权覆盖整棵来源树：查派生表时内层表也要有权限，只有外层引用的表有权限不够。
+
 事务：
 
 - `BEGIN`（或 `START TRANSACTION`）开始显式事务，`COMMIT` 提交，`ROLLBACK` 回滚。