Wrong result with hash join and join_cache_level=6

[Philip Stoev]

In maria-5.3 , the following query:

SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

returns no rows even though 1 row matches the WHERE predicate and is returned by all other plans.

explain:

id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 2
1 SIMPLE t2 ref f3 f3 5 const 1 Using where; Using join buffer (flat, BNLH join)

test case:

CREATE TABLE t1 (f2 int(11), f4 varchar(10)) ;
INSERT IGNORE INTO t1 VALUES ('19','time'),('24','juabngoyrt');

CREATE TABLE t2 (f5 varchar(10), f2 int(11), f1 int(11), f3 int(11), KEY (f3)) ;
INSERT IGNORE INTO t2 VALUES ('time','4',NULL,NULL);

SET SESSION join_cache_level=6;
SET SESSION optimizer_switch='join_cache_bka=off';
SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;
EXPLAIN SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

SET SESSION join_cache_level=0;
SET SESSION optimizer_switch='index_condition_pushdown=off';
SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

Even though this particular test case includes join_cache_bka=off, the problematic query plan was also observed without having to force it.

[Philip Stoev (philip-stoev)]

bzr version-info:

revision-id: <email address hidden>
date: 2010-12-25 18:54:14 -0800
build-date: 2010-12-26 12:03:40 +0200
revno: 2871
branch-nick: maria-5.3

[Igor Babaev (igorb-seattle)]

The bug can be reproduced with join_cache_level=4, without STRAIGHT_JOIN and
with tables of a simpler structure:

MariaDB [test]> CREATE TABLE t1 (a int PRIMARY KEY);
Query OK, 0 rows affected (0.02 sec)

MariaDB [test]> INSERT INTO t1 VALUES
    -> (7), (4), (9), (1), (3), (8), (2);
Query OK, 7 rows affected (0.01 sec)
Records: 7 Duplicates: 0 Warnings: 0

MariaDB [test]> CREATE TABLE t2 (a int, b int, INDEX idx (a));
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> INSERT INTO t2 VALUES
    -> (NULL,10), (4,80), (7,70), (6,11), (7,90), (NULL,40),
    -> (4,77), (4,50), (NULL,41), (7,99), (7,88), (8,12),
    -> (1,21), (4,90), (7,91), (8,22), (6,92), (NULL,42),
    -> (2,78), (2,51), (1,43), (5,97), (5,89);
Query OK, 23 rows affected (0.00 sec)
Records: 23 Duplicates: 0 Warnings: 0

MariaDB [test]>
MariaDB [test]> SET SESSION join_cache_level = 1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> EXPLAIN
    -> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------+
| 1 | SIMPLE | t1 | range | PRIMARY | PRIMARY | 4 | NULL | 3 | Using where; Using index |
| 1 | SIMPLE | t2 | ref | idx | idx | 5 | const | 4 | Using index condition |
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------+
2 rows in set (0.00 sec)

MariaDB [test]> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+---+------+------+
| a | a | b |
+---+------+------+
| 1 | NULL | 10 |
| 1 | NULL | 40 |
| 1 | NULL | 41 |
| 1 | NULL | 42 |
| 2 | NULL | 10 |
| 2 | NULL | 40 |
| 2 | NULL | 41 |
| 2 | NULL | 42 |
+---+------+------+
8 rows in set (0.00 sec)

MariaDB [test]> SET SESSION join_cache_level = 4;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> EXPLAIN
    -> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------------------------------+
| 1 | SIMPLE | t1 | range | PRIMARY | PRIMARY | 4 | NULL | 3 | Using where; Using index |
| 1 | SIMPLE | t2 | ref | idx | idx | 5 | const | 4 | Using where; Using join buffer (flat, BNLH join) |
+----+-------------+-------+-------+---------------+---------+---------+-------+------+--------------------------------------------------+
2 rows in set (0.00 sec)

MariaDB [test]> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
Empty set (0.00 sec)