完成语义检查，整理项目

chusql-engine/src/ChuSQL/Syntax/AST.hs

@@ -0,0 +1,49 @@
+module ChuSQL.Syntax.AST (Query (..), FromClause (..), Expr (..), SortDir (..), makeSelect) where
+
+-- 查询语句
+data Query
+    = Select
+        { selectCols :: [String]
+        , selectFrom :: FromClause
+        , selectWhere :: Maybe Expr
+        , selectOrderBy :: [(String, SortDir)]
+        , selectLimit :: Maybe Int
+        }
+    | Insert String [String] [Expr]
+    | Delete String (Maybe Expr)
+    | Update String [(String, Expr)] (Maybe Expr)
+    deriving (Show, Eq)
+
+-- 从句
+data FromClause
+    = FromTable (Maybe String) String
+    | FromJoin FromClause (Maybe String) String Expr
+    deriving (Show, Eq)
+
+-- 条件表达式
+data Expr
+    = Col String
+    | LitInt Int
+    | LitStr String
+    | LitBool Bool
+    | Gt Expr Expr
+    | Lt Expr Expr
+    | Eq Expr Expr
+    | And Expr Expr
+    | Or Expr Expr
+    deriving (Show, Eq)
+
+data SortDir
+    = Asc
+    | Desc
+    deriving (Show, Eq)
+
+makeSelect :: [String] -> String -> Maybe Expr -> Query
+makeSelect cols tbl w =
+    Select
+        { selectCols = cols
+        , selectFrom = FromTable Nothing tbl
+        , selectWhere = w
+        , selectOrderBy = []
+        , selectLimit = Nothing
+        }