MDEV-16357 LIMIT and ORDER BY clause is ignored on a query with UNION

           when using brackets

Do not create master unit for select if it has already one.

mysql-test/main/brackets.result

@@ -219,4 +219,28 @@ select 1 union select 1 union select 1;
 ((select 1) union (select 1) union (select 1));
 1
 1
+#
+# MDEV-16357: union in brackets with tail
+#             union with tail in brackets
+#
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES(1),(2),(3),(4);
+CREATE TABLE t2 (a int);
+INSERT INTO t2 VALUES (4),(5),(6),(7);
+(SELECT a FROM t1  UNION SELECT a FROM t2) LIMIT 1;
+a
+1
+(SELECT a FROM t1  UNION SELECT a FROM t2) ORDER BY a DESC;
+a
+7
+6
+5
+4
+3
+2
+1
+(SELECT a FROM t1  UNION SELECT a FROM t2 LIMIT 1);
+a
+1
+DROP TABLE t1,t2;
 # End of 10.4 tests

mysql-test/main/brackets.test

@@ -88,5 +88,23 @@ select 1 union select 1 union select 1;
 (select 1 union select 1 union select 1);
 ((select 1) union (select 1) union (select 1));
 
+--echo #
+--echo # MDEV-16357: union in brackets with tail
+--echo #             union with tail in brackets
+--echo #
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES(1),(2),(3),(4);
+
+CREATE TABLE t2 (a int);
+INSERT INTO t2 VALUES (4),(5),(6),(7);
+
+(SELECT a FROM t1  UNION SELECT a FROM t2) LIMIT 1;
+(SELECT a FROM t1  UNION SELECT a FROM t2) ORDER BY a DESC;
+
+(SELECT a FROM t1  UNION SELECT a FROM t2 LIMIT 1);
+
+DROP TABLE t1,t2;
+
 --echo # End of 10.4 tests
 

sql/sql_lex.cc

@@ -5250,6 +5250,9 @@ LEX::create_unit(SELECT_LEX *first_sel)
   SELECT_LEX_UNIT *unit;
   DBUG_ENTER("LEX::create_unit");
 
+  if (first_sel->master_unit())
+    DBUG_RETURN(first_sel->master_unit());
+
   if (!(unit= alloc_unit()))
     DBUG_RETURN(NULL);