Fixed LP bug #601156

The cause for this bug is that MariaDB 5.3 still processes derived tables
(subqueries in the FROM clause) by fully executing them during the parse
phase. This will be remedied by MWL#106 once merged into the main 5.3.

The assert statement is triggered when MATERIALIZATION is ON for EXPLAIN
EXTENDED for derived tables with an IN subquery as follows:
- mysql_parse calls JOIN::exec for the derived table as if it is regular
  execution (not explain).
- When materialization is ON, this call goes all the way to
  subselect_hash_sj_engine::exec, which creates a partial match engine
  because of NULL presence.
- In order to proceed with normal execution, the hash_sj engine substitutes
  itself with the created partial match engine.
- After the parse phase it turns out that this execution was part of
  EXPLAIN EXTENDED, which in turn calls
  Item_cond::print -> ... -> Item_subselect::print,
  which calls engine->print().
  Since subselect_hash_sj_engine::exec substituted the current
  Item_subselect engine with a  partial match engine, eventually we call
  its ::print() method. However the partial match engines are designed only
  for execution, hence there is no implementation of this print() method.

The fix temporarily removes the assert, until this code is merged with
MWL#106.

3 files changed, 45 insertions, 5 deletions

diff --git a/mysql-test/r/subselect_partial_match.result b/mysql-test/r/subselect_partial_match.result
index 7d4a3d750e1..476ec4d3bc5 100644
--- a/mysql-test/r/subselect_partial_match.result
+++ b/mysql-test/r/subselect_partial_match.result
@@ -1,5 +1,7 @@
 drop table if exists t1, t2;
-#launchpad BUG#608744
+#
+# LP BUG#608744
+#
 set @save_optimizer_switch=@@optimizer_switch;
 set @@optimizer_switch="materialization=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=off";
 create table t1 (a1 char(1), a2 char(1));
@@ -10,3 +12,22 @@ select * from t1 where (a1, a2) NOT IN (select b1, b2 from t2);
 a1	a2
 drop table t1,t2;
 set @@optimizer_switch=@save_optimizer_switch;
+#
+# LP BUG#601156
+#
+CREATE TABLE t1 (a1 int DEFAULT NULL, a2 int DEFAULT NULL);
+INSERT INTO t1 VALUES (NULL,2);
+INSERT INTO t1 VALUES (4,NULL);
+CREATE TABLE t2 (b1 int DEFAULT NULL, b2 int DEFAULT NULL);
+INSERT INTO t2 VALUES (6,NULL);
+INSERT INTO t2 VALUES (NULL,0);
+SET @@optimizer_switch='materialization=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=on';
+EXPLAIN EXTENDED
+SELECT * FROM (SELECT * FROM t1 WHERE a1 NOT IN (SELECT b2 FROM t2)) table1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived2>	system	NULL	NULL	NULL	NULL	0	0.00	const row not found
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1003	select NULL AS `a1`,NULL AS `a2` from (select `test`.`t1`.`a1` AS `a1`,`test`.`t1`.`a2` AS `a2` from `test`.`t1` where (not(<expr_cache><`test`.`t1`.`a1`>(<in_optimizer>(`test`.`t1`.`a1`,`test`.`t1`.`a1` in ()))))) `table1`
+DROP TABLE t1, t2;
diff --git a/mysql-test/t/subselect_partial_match.test b/mysql-test/t/subselect_partial_match.test
index 0b6af684003..7e573f9c614 100644
--- a/mysql-test/t/subselect_partial_match.test
+++ b/mysql-test/t/subselect_partial_match.test
@@ -7,9 +7,9 @@
 drop table if exists t1, t2;
 --enable_warnings
 
-#
---echo #launchpad BUG#608744
-#
+--echo #
+--echo # LP BUG#608744
+--echo #
 set @save_optimizer_switch=@@optimizer_switch;
 set @@optimizer_switch="materialization=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=off";
 create table t1 (a1 char(1), a2 char(1));
@@ -19,3 +19,22 @@ insert into t2 values ('a','b'), ('c', 'd');
 select * from t1 where (a1, a2) NOT IN (select b1, b2 from t2);
 drop table t1,t2;
 set @@optimizer_switch=@save_optimizer_switch;
+
+
+--echo #
+--echo # LP BUG#601156
+--echo #
+
+CREATE TABLE t1 (a1 int DEFAULT NULL, a2 int DEFAULT NULL);
+INSERT INTO t1 VALUES (NULL,2);
+INSERT INTO t1 VALUES (4,NULL);
+CREATE TABLE t2 (b1 int DEFAULT NULL, b2 int DEFAULT NULL);
+INSERT INTO t2 VALUES (6,NULL);
+INSERT INTO t2 VALUES (NULL,0);
+
+SET @@optimizer_switch='materialization=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=on';
+
+EXPLAIN EXTENDED
+SELECT * FROM (SELECT * FROM t1 WHERE a1 NOT IN (SELECT b2 FROM t2)) table1;
+
+DROP TABLE t1, t2;
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 2cc7ccfceaa..de8430cc8eb 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -4722,8 +4722,8 @@ void subselect_partial_match_engine::print(String *str,
   /*
     Should never be called as the actual engine cannot be known at query
     optimization time.
+    DBUG_ASSERT(FALSE);
   */
-  DBUG_ASSERT(FALSE);
 }