Wrong result from a query with GROUP BY, ORDER BY and LIMIT

[Igor Babaev]

The following sequence of commands gives a wrong result set:

CREATE TABLE t1 (
  id BIGINT(20) , member_id_to INT(11) , r_date DATE ,
  PRIMARY KEY (id,r_date), KEY r_date_idx (r_date), KEY t1_idx01 (member_id_to)
 ) ENGINE=InnoDB;

INSERT INTO t1 VALUES
(107924526,518491,'2011-05-01'), (107924527,518491,'2011-05-01'), (107924528,518491,'2011-05-01'),
(107924529,518491,'2011-05-01'), (107924530,518491,'2011-05-01'), (107924531,518491,'2011-05-01'),
(107924532,518491,'2011-05-01'), (107924534,518491,'2011-06-21'), (107924535,518491,'2011-06-21'), (107924536,518491,'2011-06-21'), (107924537,518491,'2011-06-21'), (107924538,518491,'2011-06-21'),
(107924542,1601319,'2011-06-21'), (107924543,1601319,'2011-06-21'), (107924544,1601319,'2011-06-21'),
(107924545,1601319,'2011-06-21'), (107924546,1601319,'2011-06-21'), (107924547,1601319,'2011-06-21'),
(107924548,1601319,'2011-06-21'), (107924549,1601319,'2011-06-21'), (107924550,1601319,'2011-06-21');

SELECT member_id_to, COUNT(*) FROM t1
    WHERE r_date = '2011-06-21' GROUP BY member_id_to ORDER BY 2 LIMIT;

MariaDB [test]> SELECT member_id_to, COUNT(*) FROM t1 WHERE r_date = '2011-06-21' GROUP BY member_id_to ORDER BY 2 LIMIT 1;
+--------------+----------+
| member_id_to | COUNT(*) |
+--------------+----------+
| NULL | 2 |
+--------------+----------+

(see also bug #12713907 reported for mysql-5.1)