Wrong result with GROUP BY and LEFT OUTER JOIN

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Server version: 10.0.8-MariaDB-log Source distribution

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MariaDB [(none)]> create database test;

Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> use test;

Database changed

MariaDB [test]> CREATE TABLE t (id bigint(20), name varchar(30),

parent bigint(20), primary key (id)) ENGINE=InnoDB;

Query OK, 0 rows affected (0.27 sec)

MariaDB [test]> INSERT INTO t values (1, 'a', NULL), (4, 'b', 1), (5,

'c', 4), (10, 'd', 1);

Query OK, 4 rows affected (0.04 sec)

Records: 4  Duplicates: 0  Warnings: 0

MariaDB [test]> SELECT t1.id, t1.name, t2.id, t2.name FROM t t1 LEFT

OUTER JOIN t t2 ON (t1.parent = t2.id and t2.name <> 'a') GROUP BY

t1.id;

+----+------+------+------+

| id | name | id   | name |

+----+------+------+------+

|  1 | a    | NULL | NULL |

|  4 | b    | NULL | NULL |

|  5 | c    | NULL | NULL |

| 10 | d    | NULL | NULL |

+----+------+------+------+

4 rows in set (0.00 sec)

MariaDB [test]> SELECT t1.id, t1.name, t2.id, t2.name FROM t t1 LEFT

OUTER JOIN t t2 ON (t1.parent = t2.id and t2.name <> 'a');

+----+------+------+------+

| id | name | id   | name |

+----+------+------+------+

|  1 | a    | NULL | NULL |

|  4 | b    | NULL | NULL |

|  5 | c    |    4 | b    |

| 10 | d    | NULL | NULL |

+----+------+------+------+

4 rows in set (0.00 sec)

MariaDB [test]> SELECT t1.id, t1.name, t2.id, t2.name FROM t t1 LEFT

OUTER JOIN t t2 ON (t1.parent = t2.id and t2.name <> 'a') GROUP BY

t1.id, t1.name;

+----+------+------+------+

| id | name | id   | name |

+----+------+------+------+

|  1 | a    | NULL | NULL |

|  4 | b    | NULL | NULL |

|  5 | c    |    4 | b    |

| 10 | d    | NULL | NULL |

+----+------+------+------+

4 rows in set (0.00 sec)

MariaDB [test]> SELECT t1.id, t1.name, t2.id, t2.name FROM t t1 LEFT

OUTER JOIN t t2 ON (t1.parent = t2.id) GROUP BY t1.id;

+----+------+------+------+

| id | name | id   | name |

+----+------+------+------+

|  1 | a    | NULL | NULL |

|  4 | b    |    1 | a    |

|  5 | c    |    4 | b    |

| 10 | d    |    1 | a    |

+----+------+------+------+

4 rows in set (0.00 sec)