MDEV-19363 Assertion `select_lex' failed in LEX::pop_select

This patch corrects the patch for MDEV-19324. The latter did not
work properly in the cases when the transformation
  (SELECT ... ORDER BY ...) LIMIT ... =>
   SELECT ... ORDER BY ... LIMIT ...
was applied to the operands of a set operation.

1 files changed, 59 insertions, 0 deletions

diff --git a/mysql-test/main/brackets.result b/mysql-test/main/brackets.result
index 3cf3468320f..869afe56c9c 100644
--- a/mysql-test/main/brackets.result
+++ b/mysql-test/main/brackets.result
@@ -393,4 +393,63 @@ EXPLAIN
   }
 }
 drop table t1;
+#
+# MDEV-19363: ((SELECT ...) ORDER BY col ) LIMIT n UNION ...
+#
+create table t1 (pk int);
+insert into t1 values (5),(4),(1),(2),(3);
+((select * from t1 order by pk) limit 2) union (select * from t1 where pk > 4);
+pk
+1
+2
+5
+explain extended ((select * from t1 order by pk) limit 2) union (select * from t1 where pk > 4);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	5	100.00	Using filesort
+2	UNION	t1	ALL	NULL	NULL	NULL	NULL	5	100.00	Using where
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	NULL	
+Warnings:
+Note	1003	(/* select#1 */ select `test`.`t1`.`pk` AS `pk` from `test`.`t1` order by `test`.`t1`.`pk` limit 2) union (/* select#2 */ select `test`.`t1`.`pk` AS `pk` from `test`.`t1` where `test`.`t1`.`pk` > 4)
+explain format=json ((select * from t1 order by pk) limit 2) union (select * from t1 where pk > 4);
+EXPLAIN
+{
+  "query_block": {
+    "union_result": {
+      "table_name": "<union1,2>",
+      "access_type": "ALL",
+      "query_specifications": [
+        {
+          "query_block": {
+            "select_id": 1,
+            "read_sorted_file": {
+              "filesort": {
+                "sort_key": "t1.pk",
+                "table": {
+                  "table_name": "t1",
+                  "access_type": "ALL",
+                  "rows": 5,
+                  "filtered": 100
+                }
+              }
+            }
+          }
+        },
+        {
+          "query_block": {
+            "select_id": 2,
+            "operation": "UNION",
+            "table": {
+              "table_name": "t1",
+              "access_type": "ALL",
+              "rows": 5,
+              "filtered": 100,
+              "attached_condition": "t1.pk > 4"
+            }
+          }
+        }
+      ]
+    }
+  }
+}
+drop table t1;
 # End of 10.4 tests