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, 35 insertions, 0 deletions

diff --git a/mysql-test/t/union.test b/mysql-test/t/union.test
index 240115837c7..8ef8f7c4017 100644
--- a/mysql-test/t/union.test
+++ b/mysql-test/t/union.test
@@ -1437,3 +1437,38 @@ SET @advertAcctId = 1000003;
 select @advertAcctId as a from dual union all select 1.0 from dual;
 
 --echo End of 5.5 tests
+
+--echo #
+--echo # MDEV-13784: query causes seg fault
+--echo #
+
+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);
+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);
+drop table t1, t2, t3, t4, t5;