MSSQL: Support standalone BEGIN...END blocks

Signed-off-by: Guan-Ming (Wesley) Chiu <105915352+guan404ming@users.noreply.github.com>

Author: guan404ming

src/dialect/mssql.rs

@@ -145,7 +145,22 @@ impl Dialect for MsSqlDialect {
     }
 
     fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
-        if parser.peek_keyword(Keyword::IF) {
+        if parser.parse_keyword(Keyword::BEGIN) {
+            if parser.peek_keyword(Keyword::TRANSACTION)
+                || parser.peek_keyword(Keyword::WORK)
+                || parser.peek_keyword(Keyword::TRY)
+                || parser.peek_keyword(Keyword::CATCH)
+                || parser.peek_keyword(Keyword::DEFERRED)
+                || parser.peek_keyword(Keyword::IMMEDIATE)
+                || parser.peek_keyword(Keyword::EXCLUSIVE)
+                || parser.peek_token_ref().token == Token::SemiColon
+                || parser.peek_token_ref().token == Token::EOF
+            {
+                parser.prev_token();
+                return None;
+            }
+            return Some(parser.parse_begin_exception_end());
+        } else if parser.peek_keyword(Keyword::IF) {
             Some(self.parse_if_stmt(parser))
         } else if parser.parse_keywords(&[Keyword::CREATE, Keyword::TRIGGER]) {
             Some(self.parse_create_trigger(parser, false))

tests/sqlparser_mssql.rs

@@ -2554,3 +2554,74 @@ fn test_sql_keywords_as_column_aliases() {
         }
     }
 }
+
+#[test]
+fn parse_mssql_begin_end_block() {
+    // Single statement
+    let sql = "BEGIN SELECT 1; END";
+    let stmt = ms().verified_stmt(sql);
+    match &stmt {
+        Statement::StartTransaction {
+            begin,
+            has_end_keyword,
+            statements,
+            transaction,
+            modifier,
+            ..
+        } => {
+            assert!(begin);
+            assert!(has_end_keyword);
+            assert!(transaction.is_none());
+            assert!(modifier.is_none());
+            assert_eq!(statements.len(), 1);
+        }
+        _ => panic!("Expected StartTransaction, got: {stmt:?}"),
+    }
+
+    // Multiple statements
+    let sql = "BEGIN SELECT 1; SELECT 2; END";
+    let stmt = ms().verified_stmt(sql);
+    match &stmt {
+        Statement::StartTransaction {
+            statements,
+            has_end_keyword,
+            ..
+        } => {
+            assert!(has_end_keyword);
+            assert_eq!(statements.len(), 2);
+        }
+        _ => panic!("Expected StartTransaction, got: {stmt:?}"),
+    }
+
+    // DML inside BEGIN/END
+    let sql = "BEGIN INSERT INTO t VALUES (1); UPDATE t SET x = 2; END";
+    let stmt = ms().verified_stmt(sql);
+    match &stmt {
+        Statement::StartTransaction {
+            statements,
+            has_end_keyword,
+            ..
+        } => {
+            assert!(has_end_keyword);
+            assert_eq!(statements.len(), 2);
+        }
+        _ => panic!("Expected StartTransaction, got: {stmt:?}"),
+    }
+
+    // BEGIN TRANSACTION still works
+    let sql = "BEGIN TRANSACTION";
+    let stmt = ms().verified_stmt(sql);
+    match &stmt {
+        Statement::StartTransaction {
+            begin,
+            has_end_keyword,
+            transaction,
+            ..
+        } => {
+            assert!(begin);
+            assert!(!has_end_keyword);
+            assert!(transaction.is_some());
+        }
+        _ => panic!("Expected StartTransaction, got: {stmt:?}"),
+    }
+}