MDEV-275: SHOW EXPLAIN: server crashes in JOIN::print_explain with IN subquery...

MDEV-275: SHOW EXPLAIN: server crashes in JOIN::print_explain with IN subquery and aggregate function
- Don't try to produce plans after JOIN::cleanup() has been called, because:
   = JOIN::cleanup leaves data structures in partially-cleaned state
   = Walking them is hazardous (see this bug), and has funny effects
     (See previous commits, "Using join cache" may or may not be shown)
   = Changing data structures to be persisted may cause unwanted side effects
- The consequence is that SHOW EXPLAIN will show "Query plan already deleted" when e.g. 
  reading data after filesort.

mysql-test/r/show_explain.result

@@ -154,8 +154,7 @@ set debug_dbug='d,show_explain_probe_join_exec_end';
 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	a	ALL	NULL	NULL	NULL	NULL	10	
-2	DEPENDENT SUBQUERY	b	ALL	NULL	NULL	NULL	NULL	10	
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
 a	(select max(a) from t0 b where b.a+a.a<10)
@@ -208,13 +207,13 @@ Note	1003	select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	3	
-2	DEPENDENT SUBQUERY	t0	ALL	NULL	NULL	NULL	NULL	10	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	3	
-2	DEPENDENT SUBQUERY	t0	ALL	NULL	NULL	NULL	NULL	10	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
 a	SUBQ
@@ -312,8 +311,7 @@ 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	
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a
 a
@@ -404,7 +402,7 @@ set debug_dbug='d,show_explain_probe_join_exec_end';
 select * from t0 where 1>10;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	select * from t0 where 1>10
 a
@@ -419,7 +417,7 @@ set debug_dbug='d,show_explain_probe_join_exec_end';
 select * from t0,t3 where t3.a=112233;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
 Warnings:
 Note	1003	select * from t0,t3 where t3.a=112233
 a	a
@@ -515,4 +513,26 @@ count(*)
 1740
 set debug_dbug='';
 drop table t2, t3, t4;
+#
+# MDEV-275: SHOW EXPLAIN: server crashes in JOIN::print_explain with IN subquery and aggregate function
+#
+CREATE TABLE t2 ( `pk` INT NOT NULL PRIMARY KEY, `a1` INT NOT NULL, KEY(`a1`)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES 
+(1,5),(2,4),(3,6),(4,9),(5,2),(6,8),(7,4),(8,8),(9,0),(10,43),
+(11,23),(12,3),(13,45),(14,16),(15,2),(16,33),(17,2),(18,5),(19,9),(20,2);
+set @show_explain_probe_select_id=1;
+set debug='d,show_explain_probe_join_exec_end';
+Warnings:
+Warning	1287	The syntax '@@debug' is deprecated and will be removed in MariaDB 5.6. Please use '@@debug_dbug' instead
+SELECT * FROM t2 WHERE (5, 78) IN (SELECT `a1`, MAX(`a1`) FROM t2 GROUP BY `a1`);
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
+Warnings:
+Note	1003	SELECT * FROM t2 WHERE (5, 78) IN (SELECT `a1`, MAX(`a1`) FROM t2 GROUP BY `a1`)
+pk	a1
+set debug='';
+Warnings:
+Warning	1287	The syntax '@@debug' is deprecated and will be removed in MariaDB 5.6. Please use '@@debug_dbug' instead
+DROP TABLE t2;
 drop table t0,t1;

mysql-test/t/show_explain.test

@@ -499,6 +499,28 @@ reap;
 set debug_dbug='';
 drop table t2, t3, t4;
 
+--echo #
+--echo # MDEV-275: SHOW EXPLAIN: server crashes in JOIN::print_explain with IN subquery and aggregate function
+--echo #
+CREATE TABLE t2 ( `pk` INT NOT NULL PRIMARY KEY, `a1` INT NOT NULL, KEY(`a1`)) ENGINE=MyISAM; 
+INSERT INTO t2 VALUES 
+  (1,5),(2,4),(3,6),(4,9),(5,2),(6,8),(7,4),(8,8),(9,0),(10,43),
+  (11,23),(12,3),(13,45),(14,16),(15,2),(16,33),(17,2),(18,5),(19,9),(20,2);
+
+set @show_explain_probe_select_id=1;
+set debug='d,show_explain_probe_join_exec_end';
+send
+  SELECT * FROM t2 WHERE (5, 78) IN (SELECT `a1`, MAX(`a1`) FROM t2 GROUP BY `a1`);
+connection default;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+connection con1;
+reap;
+set debug='';
+
+DROP TABLE t2;
+
+
 ## TODO: Test this: have several SHOW EXPLAIN requests be queued up for a
 ##       thread and served together.
 

sql/sql_select.cc

@@ -10569,8 +10569,9 @@ void JOIN::cleanup(bool full)
   
   /*
     psergey: let's try without this first:
-    have_query_plan= QEP_DELETED;
   */
+  have_query_plan= QEP_DELETED;
+
   if (table)
   {
     JOIN_TAB *tab;