Fix(parser,bigquery): make separator optional in STRING_AGG parser (#…

…1974)

* Fix(parser,bigquery): make separator optional in STRING_AGG parser

* Refactor

sqlglot/parser.py

@@ -3861,13 +3861,11 @@ def _parse_string_agg(self) -> exp.Expression:
             args = self._parse_csv(self._parse_conjunction)
 
         index = self._index
-        if not self._match(TokenType.R_PAREN):
+        if not self._match(TokenType.R_PAREN) and args:
             # postgres: STRING_AGG([DISTINCT] expression, separator [ORDER BY expression1 {ASC | DESC} [, ...]])
-            return self.expression(
-                exp.GroupConcat,
-                this=seq_get(args, 0),
-                separator=self._parse_order(this=seq_get(args, 1)),
-            )
+            # bigquery: STRING_AGG([DISTINCT] expression [, separator] [ORDER BY key [{ASC | DESC}] [, ... ]] [LIMIT n])
+            args[-1] = self._parse_limit(this=self._parse_order(this=args[-1]))
+            return self.expression(exp.GroupConcat, this=args[0], separator=seq_get(args, 1))
 
         # Checks if we can parse an order clause: WITHIN GROUP (ORDER BY <order_by_expression_list> [ASC | DESC]).
         # This is done "manually", instead of letting _parse_window parse it into an exp.WithinGroup node, so that

tests/dialects/test_bigquery.py

@@ -29,6 +29,7 @@ def test_bigquery(self):
         with self.assertRaises(ParseError):
             transpile("SELECT * FROM UNNEST(x) AS x(y)", read="bigquery")
 
+        self.validate_identity("STRING_AGG(DISTINCT a ORDER BY b DESC, c DESC LIMIT 10)")
         self.validate_identity("SELECT PARSE_TIMESTAMP('%c', 'Thu Dec 25 07:30:00 2008', 'UTC')")
         self.validate_identity("SELECT ANY_VALUE(fruit HAVING MAX sold) FROM fruits")
         self.validate_identity("SELECT ANY_VALUE(fruit HAVING MIN sold) FROM fruits")