fix group_by

corpus/select_statement/select.txt

@@ -129,6 +129,24 @@ group by
 select name from items group by 1, 2;
 --------------------------------------------------------------------------------
 
+(source_file
+  (select_statement
+    (select_item
+      (identifier))
+    (select_from
+      (from_item
+        (from_table
+          (identifier))))
+    (select_group_by
+      (number)
+      (number))))
+
+================================================================================
+group by with parens
+================================================================================
+select name from items group by (1, 2);
+--------------------------------------------------------------------------------
+
 (source_file
   (select_statement
     (select_item

grammar.js

@@ -511,7 +511,13 @@ module.exports = grammar({
       kw("offset"), $._value_expression,
       optional(choice(kw("row"), kw("rows")))
     ),
-    select_group_by: $ => seq(kw("group"), kw("by"), commaSep1($._value_expression)),
+    // TODO(chrde): rollup, cube, grouping sets
+    select_group_by: $ => prec(1, seq(kw("group"), kw("by"),
+      choice(
+        seq("(", commaSep1($._value_expression), ")"),
+        commaSep1($._value_expression),
+      ),
+    )),
     select_order_by: $ => seq(kw("order"), kw("by"), commaSep1($.order_by_item)),
     order_by_item: $ => seq($._value_expression, optional($.order_by_direction)),
     order_by_direction: $ => choice(kw("asc"), kw("desc")),