From fd3e9c53c1b3c50ae85d020551915d5a31cd3044 Mon Sep 17 00:00:00 2001
From: Sergey Petrunya <psergey@askmonty.org>
Date: Wed, 1 Aug 2012 15:51:52 +0400
Subject: [PATCH] MDEV-423: SHOW EXPLAIN: 'Using where' for a subquery is shown
 in EXPLAIN, but not in SHOW EXPLAIN - Take into account that the optimizer
 may run the subquery, delete it,   and then make a JOIN::optimize call again.

---
 mysql-test/r/show_explain.result | 34 +++++++++++++++++++++++++++++
 mysql-test/t/show_explain.test   | 37 ++++++++++++++++++++++++++++++++
 sql/sql_select.cc                | 10 +++++++--
 3 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/mysql-test/r/show_explain.result b/mysql-test/r/show_explain.result
index 6ff9a0d0f4e..2f7de62e7fe 100644
--- a/mysql-test/r/show_explain.result
+++ b/mysql-test/r/show_explain.result
@@ -998,5 +998,39 @@ Note	1003	SELECT b AS field1, b AS field2 FROM t1, t2, t3 WHERE d = b ORDER BY f
 field1	field2
 set debug_dbug='';
 DROP TABLE t1,t2,t3;
+#
+# MDEV-423: SHOW EXPLAIN: 'Using where' for a subquery is shown in EXPLAIN, but not in SHOW EXPLAIN output
+#
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (7),(0),(9),(3),(4),(2),(5),(7),(0),(9),(3),(4),(2),(5);
+CREATE TABLE t2 (b INT, c INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES 
+(0,4),(8,6),(1,3),(8,5),(9,3),(24,246),(6,2),(1,9),(6,3),(2,8),
+(4,1),(8,8),(4,8),(4,5),(7,7),(4,5),(1,1),(9,6),(4,2),(8,9);
+create table t3 like t2;
+insert into t3 select * from t2;
+explain 
+SELECT max(a+b+c) FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias 
+WHERE EXISTS ( SELECT * FROM t3 WHERE b = c )  OR a <= 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	14	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	20	
+3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	20	Using where
+set @show_explain_probe_select_id=1;
+set debug_dbug='d,show_explain_probe_join_exec_start';
+SELECT max(a+b+c) FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias 
+WHERE EXISTS ( SELECT * FROM t3 WHERE b = c )  OR a <= 10;
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	14	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	20	
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Query plan already deleted
+Warnings:
+Note	1003	SELECT max(a+b+c) FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias 
+WHERE EXISTS ( SELECT * FROM t3 WHERE b = c )  OR a <= 10
+max(a+b+c)
+279
+set debug_dbug='';
+DROP TABLE t1,t2,t3;
 # End
 drop table t0;
diff --git a/mysql-test/t/show_explain.test b/mysql-test/t/show_explain.test
index 24b01402287..485bda84cf5 100644
--- a/mysql-test/t/show_explain.test
+++ b/mysql-test/t/show_explain.test
@@ -1026,5 +1026,42 @@ set debug_dbug='';
 
 DROP TABLE t1,t2,t3;
 
+
+--echo #
+--echo # MDEV-423: SHOW EXPLAIN: 'Using where' for a subquery is shown in EXPLAIN, but not in SHOW EXPLAIN output
+--echo #
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (7),(0),(9),(3),(4),(2),(5),(7),(0),(9),(3),(4),(2),(5);		
+
+CREATE TABLE t2 (b INT, c INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES 
+(0,4),(8,6),(1,3),(8,5),(9,3),(24,246),(6,2),(1,9),(6,3),(2,8),
+(4,1),(8,8),(4,8),(4,5),(7,7),(4,5),(1,1),(9,6),(4,2),(8,9);
+
+create table t3 like t2;
+insert into t3 select * from t2;
+
+explain 
+SELECT max(a+b+c) FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias 
+WHERE EXISTS ( SELECT * FROM t3 WHERE b = c )  OR a <= 10;
+
+set @show_explain_probe_select_id=1;
+set debug_dbug='d,show_explain_probe_join_exec_start';
+
+send
+SELECT max(a+b+c) FROM t1 AS alias1, ( SELECT * FROM t2 ) AS alias 
+WHERE EXISTS ( SELECT * FROM t3 WHERE b = c )  OR a <= 10;
+
+connection default;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+
+connection con1;
+reap;
+
+set debug_dbug='';
+
+DROP TABLE t1,t2,t3;
+
 --echo # End
 drop table t0;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 02be522290d..89765ab44db 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -987,7 +987,13 @@ err:
 int JOIN::optimize()
 {
   int res= optimize_inner();
-  if (!res)
+  /*
+    If we're inside a non-correlated subquery, this function may be 
+    called for the second time after the subquery has been executed
+    and deleted. The second call will not produce a valid query plan, it will
+    short-circuit because optimized==TRUE.
+  */
+  if (!res && have_query_plan != QEP_DELETED)
     have_query_plan= QEP_AVAILABLE;
   return res;
 }
@@ -21630,7 +21636,7 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
   DBUG_PRINT("info", ("Select 0x%lx, type %s, message %s",
 		      (ulong)join->select_lex, join->select_lex->type,
 		      message ? message : "NULL"));
-  DBUG_ASSERT(have_query_plan == QEP_AVAILABLE);
+  DBUG_ASSERT(on_the_fly? have_query_plan == QEP_AVAILABLE: TRUE);
   /* Don't log this into the slow query log */
 
   if (!on_the_fly)