[#MDEV-5071] [5.1-5.2 only] Wrong result (missing rows) with group by, multi-part key, equality conditions (MySQL:70359)

The bug also exists in MariaDB 5.3.12, but it has been fixed in the current 5.3 tree. It still exists in 5.1 and 5.2 tree though. It also exists in all of 5.1-5.7 to date. I'm filing it for the record, to make it easier to find.

CREATE TABLE t1 (a INT, b VARCHAR(1), INDEX(b,a)) ENGINE=MyISAM;

INSERT INTO t1 VALUES (2,'s'),(5,'h'),(3,'q'),(1,'a'),(3,'v'),

(6,'u'),(7,'s'),(5,'y'),(1,'z'),(5,'i'),(2,'y');

SELECT b, max(a) FROM t1 WHERE b = 'i' OR a = 2 GROUP BY b;

Actual result:

SELECT b, max(a) FROM t1 WHERE b = 'i' OR a = 2 GROUP BY b;

b	max(a)

i	5

Expected result:

b	max(a)

i	5

s	2

y	2

EXPLAIN:

EXPLAIN EXTENDED

SELECT b, max(a) FROM t1 WHERE b = 'i' OR a = 2 GROUP BY b;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	range	b	b	4	NULL	6	100.00	Using where; Using index for group-by

Warnings:

Note	1003	select `test`.`t1`.`b` AS `b`,max(`test`.`t1`.`a`) AS `max(a)` from `test`.`t1` where ((`test`.`t1`.`b` = 'i') or (`test`.`t1`.`a` = 2)) group by `test`.`t1`.`b`

[MDEV-5071] [5.1-5.2 only] Wrong result (missing rows) with group by, multi-part key, equality conditions (MySQL:70359) Created: 2013-09-25 Updated: 2014-11-16 Resolved: 2014-11-16
Status:	Closed
Project:	MariaDB Server
Component/s:	Optimizer
Affects Version/s:	5.1.67, 5.2.14
Fix Version/s:	5.1.73, 5.2.15

[MDEV-5071] [5.1-5.2 only] Wrong result (missing rows) with group by, multi-part key, equality conditions (MySQL:70359) Created: 2013-09-25 Updated: 2014-11-16 Resolved: 2014-11-16