Add support for inline table valued functions for SQL Server

Author: aharpervc

src/ast/data_type.rs

@@ -48,6 +48,7 @@ pub enum DataType {
     /// Table type in [PostgreSQL], e.g. CREATE FUNCTION RETURNS TABLE(...).
     ///
     /// [PostgreSQL]: https://www.postgresql.org/docs/15/sql-createfunction.html
+    /// [MsSQL]: https://learn.microsoft.com/en-us/sql/t-sql/statements/create-function-transact-sql?view=sql-server-ver16#c-create-a-multi-statement-table-valued-function
     Table(Vec<ColumnDef>),
     /// Fixed-length character type, e.g. CHARACTER(10).
     Character(Option<CharacterLength>),
@@ -716,7 +717,12 @@ impl fmt::Display for DataType {
             DataType::Unspecified => Ok(()),
             DataType::Trigger => write!(f, "TRIGGER"),
             DataType::AnyType => write!(f, "ANY TYPE"),
-            DataType::Table(fields) => write!(f, "TABLE({})", display_comma_separated(fields)),
+            DataType::Table(fields) => {
+                if fields.is_empty() {
+                    return write!(f, "TABLE");
+                }
+                write!(f, "TABLE({})", display_comma_separated(fields))
+            }
             DataType::GeometricType(kind) => write!(f, "{}", kind),
         }
     }

src/ast/ddl.rs

@@ -2346,6 +2346,9 @@ impl fmt::Display for CreateFunction {
         if let Some(CreateFunctionBody::Return(function_body)) = &self.function_body {
             write!(f, " RETURN {function_body}")?;
         }
+        if let Some(CreateFunctionBody::AsReturn(function_body)) = &self.function_body {
+            write!(f, " AS RETURN {function_body}")?;
+        }
         if let Some(using) = &self.using {
             write!(f, " {using}")?;
         }

src/ast/mod.rs

@@ -8778,6 +8778,18 @@ pub enum CreateFunctionBody {
     ///
     /// [PostgreSQL]: https://www.postgresql.org/docs/current/sql-createfunction.html
     Return(Expr),
+
+    /// Function body expression using the 'AS RETURN' keywords
+    ///
+    /// Example:
+    /// ```sql
+    /// CREATE FUNCTION myfunc(a INT, b INT)
+    /// RETURNS TABLE
+    /// AS RETURN (SELECT a + b AS sum);
+    /// ```
+    ///
+    /// [MsSql]: https://learn.microsoft.com/en-us/sql/t-sql/statements/create-function-transact-sql
+    AsReturn(Expr),
 }
 
 #[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]

src/parser/mod.rs

@@ -5208,15 +5208,26 @@ impl<'a> Parser<'a> {
 
         self.expect_keyword_is(Keyword::AS)?;
 
-        let begin_token = self.expect_keyword(Keyword::BEGIN)?;
-        let statements = self.parse_statement_list(&[Keyword::END])?;
-        let end_token = self.expect_keyword(Keyword::END)?;
+        let function_body = if self.peek_keyword(Keyword::BEGIN) {
+            let begin_token = self.expect_keyword(Keyword::BEGIN)?;
+            let statements = self.parse_statement_list(&[Keyword::END])?;
+            let end_token = self.expect_keyword(Keyword::END)?;
 
-        let function_body = Some(CreateFunctionBody::AsBeginEnd(BeginEndStatements {
-            begin_token: AttachedToken(begin_token),
-            statements,
-            end_token: AttachedToken(end_token),
-        }));
+            Some(CreateFunctionBody::AsBeginEnd(BeginEndStatements {
+                begin_token: AttachedToken(begin_token),
+                statements,
+                end_token: AttachedToken(end_token),
+            }))
+        } else if self.peek_keyword(Keyword::RETURN) {
+            self.expect_keyword(Keyword::RETURN)?;
+            let expr = self.parse_expr()?;
+            if !matches!(expr, Expr::Subquery(_)) {
+                parser_err!("Expected a subquery after RETURN", expr.span().start)?;
+            }
+            Some(CreateFunctionBody::AsReturn(expr))
+        } else {
+            parser_err!("Unparsable function body", self.peek_token().span.start)?
+        };
 
         Ok(Statement::CreateFunction(CreateFunction {
             or_alter,
@@ -9784,8 +9795,12 @@ impl<'a> Parser<'a> {
                     Ok(DataType::AnyType)
                 }
                 Keyword::TABLE => {
-                    let columns = self.parse_returns_table_columns()?;
-                    Ok(DataType::Table(columns))
+                    if self.peek_keyword(Keyword::AS) {
+                        Ok(DataType::Table(Vec::<ColumnDef>::new()))
+                    } else {
+                        let columns = self.parse_returns_table_columns()?;
+                        Ok(DataType::Table(columns))
+                    }
                 }
                 Keyword::SIGNED => {
                     if self.parse_keyword(Keyword::INTEGER) {

tests/sqlparser_mssql.rs

@@ -288,6 +288,14 @@ fn parse_create_function() {
         END\
     ";
     let _ = ms().verified_stmt(create_function_with_return_expression);
+
+    let create_inline_table_value_function = "\
+        CREATE FUNCTION some_inline_tvf(@foo INT, @bar VARCHAR(256)) \
+        RETURNS TABLE \
+        AS \
+        RETURN (SELECT 1 AS col_1)\
+    ";
+    let _ = ms().verified_stmt(create_inline_table_value_function);
 }
 
 #[test]