MDEV-238: SHOW EXPLAIN: Server crashes in JOIN::print_explain with FROM subquery and GROUP BY

- Support SHOW EXPLAIN for selects that have "Using temporary; Using filesort".

1 files changed, 25 insertions, 0 deletions

diff --git a/mysql-test/r/show_explain.result b/mysql-test/r/show_explain.result
index 74def21585f..db1d57b7004 100644
--- a/mysql-test/r/show_explain.result
+++ b/mysql-test/r/show_explain.result
@@ -284,4 +284,29 @@ a
 7
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+set debug='';
+#
+# MDEV-238: SHOW EXPLAIN: Server crashes in JOIN::print_explain with FROM subquery and GROUP BY
+#
+CREATE TABLE t2 ( a INT );
+INSERT INTO t2 VALUES (1),(2),(1),(4),(2);
+explain SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	5	Using join buffer (flat, BNL join)
+set debug='d,show_explain_in_find_all_keys';
+SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
+# NOTE: current code will not show "Using join buffer":
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	5	
+Warnings:
+Note	1003	SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a
+a
+1
+2
+4
+set debug='';
+DROP TABLE t2;
 drop table t0,t1;