MDEV-13784: query causes seg fault

When we have a nested subquery then a subquery that was a dependent subquery
may change to an independent one when we optimizer the inner subqueries.
This is handled st_select_lex::optimize_unflattened_subqueries.
Currently a subquery that was changed to independent from dependent after optimization
phase incorrectly shows dependent in the output of Explain, this happens because we
don't update used_tables for the WHERE clause, ON clause, etc after the optimization phase.

1 files changed, 38 insertions, 0 deletions

diff --git a/mysql-test/r/union.result b/mysql-test/r/union.result
index 5ea0f975a91..9b7a361fdc5 100644
--- a/mysql-test/r/union.result
+++ b/mysql-test/r/union.result
@@ -2049,3 +2049,41 @@ a
 1000003.0
 1.0
 End of 5.5 tests
+#
+# MDEV-13784: query causes seg fault
+#
+CREATE TABLE t1 (`bug_id` int NOT NULL PRIMARY KEY, `product_id` int NOT NULL);
+INSERT INTO t1 VALUES (45199,1184);
+CREATE TABLE t2 (`product_id` int NOT NULL,`userid` int NOT NULL, PRIMARY KEY (`product_id`,`userid`));
+INSERT INTO t2 VALUES (1184,103),(1184,624),(1184,1577),(1184,1582);
+CREATE TABLE t3 (`id` int NOT NULL  PRIMARY KEY,`name` varchar(64));
+CREATE TABLE t4 ( `userid` int NOT NULL PRIMARY KEY, `login_name` varchar(255));
+INSERT INTO t4 VALUES (103,'foo'),(624,'foo'),(1577,'foo'),(1582,'foo');
+CREATE TABLE t5 (`id` int NOT NULL PRIMARY KEY, `name` varchar(64));
+explain select
+(
+select login_name from t4 where userId = (
+select userid from t2 where product_id = t1.product_id
+union
+select userid from t2 where product_id = (
+select id from t5 where name = (select name from t3 where id = t1.product_id)) limit 1 )
+) as x  from t1 where (t1.bug_id=45199);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	PRIMARY	NULL	NULL	NULL	1	
+2	SUBQUERY	t4	eq_ref	PRIMARY	PRIMARY	4	func	1	Using where
+3	SUBQUERY	t2	ref	PRIMARY	PRIMARY	4	const	3	Using index
+4	UNION	t2	ref	PRIMARY	PRIMARY	4	func	1	Using where; Using index
+5	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+6	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+NULL	UNION RESULT	<union3,4>	ALL	NULL	NULL	NULL	NULL	NULL	
+select
+(
+select login_name from t4 where userId = (
+select userid from t2 where product_id = t1.product_id
+union
+select userid from t2 where product_id = (
+select id from t5 where name = (select name from t3 where id = t1.product_id)) limit 1 )
+) as x  from t1 where (t1.bug_id=45199);
+x
+foo
+drop table t1, t2, t3, t4, t5;