[MySql] Support mixed-parenthesis syntax for unions (#3824)

Author: Naros

sql/mysql/Positive-Technologies/MySqlParser.g4

@@ -901,7 +901,8 @@ replaceStatement
 selectStatement
     : querySpecification lockClause?                                #simpleSelect
     | queryExpression lockClause?                                   #parenthesisSelect
-    | querySpecificationNointo unionStatement+
+    | (querySpecificationNointo | queryExpressionNointo)
+        unionStatement+
         (
           UNION unionType=(ALL | DISTINCT)?
           (querySpecification | queryExpression)

sql/mysql/Positive-Technologies/examples/ddl_create.sql

@@ -683,3 +683,34 @@ SELECT
      ,@N_latin;
 END
 #end
+
+#begin
+CREATE PROCEDURE test_union()
+BEGIN
+    (SELECT id FROM test_auto_inc)
+    UNION ALL
+    SELECT id FROM test_auto_inc;
+END
+#end
+
+#begin
+CREATE PROCEDURE test_union()
+BEGIN
+    (SELECT id FROM test_auto_inc)
+    UNION ALL
+    SELECT id FROM test_auto_inc
+    UNION ALL
+    SELECT id FROM test_auto_inc ORDER BY id;
+END
+#end
+
+#begin
+CREATE PROCEDURE test_union()
+BEGIN
+    (SELECT id FROM test_auto_inc)
+    UNION ALL
+    (SELECT id FROM test_auto_inc)
+    UNION ALL
+    SELECT id FROM test_auto_inc ORDER BY id;
+END
+#end