Why my mysql DISTINCT doesn't work ?
- by belaz
Hello,
Why the two query below return duplicate member_id and not the third ?
i need the second query to work with distinct.
Anytime i run a GROUP BY, this query is incredibly slow and the resultset doesn't return the same value as distinct (the value is wrong).
SELECT member_id, id
FROM ( SELECT * FROM table1 ORDER BY created_at desc ) as u
LIMIT 5
+-----------+--------+
| member_id | id |
+-----------+--------+
| 11333 | 313095 |
| 141831 | 313094 |
| 141831 | 313093 |
| 12013 | 313092 |
| 60821 | 313091 |
+-----------+--------+
SELECT distinct member_id, id
FROM ( SELECT * FROM table1 ORDER BY created_at desc ) as u
LIMIT 5
+-----------+--------+
| member_id | id |
+-----------+--------+
| 11333 | 313095 |
| 141831 | 313094 |
| 141831 | 313093 |
| 12013 | 313092 |
| 60821 | 313091 |
+-----------+--------+
SELECT distinct member_id
FROM ( SELECT * FROM table1 ORDER BY created_at desc ) as u
LIMIT 5
+-----------+
| member_id |
+-----------+
| 11333 |
| 141831 |
| 12013 |
| 60821 |
| 64980 |
+-----------+
my table sample
CREATE TABLE `table1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`member_id` int(11) NOT NULL,
`s_type_id` int(11) NOT NULL,
`created_at` datetime DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `s_FI_1` (`member_id`),
KEY `s_FI_2` (`s_type_id`)
) ENGINE=InnoDB AUTO_INCREMENT=313096 DEFAULT CHARSET=utf8;
