Delete duplicate rows having count greater than 1 in mysql - mysql

Question

Need some help on a MySQL query to delete the rows where the userID count is greater than one and has an acl value=4.
What I've tried as the select query:
DELETE FROM `users_acl`
WHERE userID IN(
SELECT * FROM `users_acl`
WHERE `acl` BETWEEN 2 AND 4
GROUP BY userID
HAVING COUNT(userID) > 1
);
But can't find a proper way to delete the rows in the same query.
Table structure
+--------+-----+---------+
| userID | acl | deleted |
+--------+-----+---------+
| 27 | 2 | 0 |
| 28 | 2 | 0 |
| 31 | 2 | 0 |
| 42 | 2 | 0 |
| 42 | 4 | 0 |
| 45 | 1 | 0 |
| 51 | 1 | 0 |
| 54 | 1 | 0 |
| 63 | 2 | 0 |
| 63 | 4 | 0 |
| 64 | 1 | 0 |
| 69 | 2 | 0 |
| 73 | 2 | 0 |
| 73 | 4 | 0 |
| 76 | 1 | 0 |
| 77 | 2 | 0 |
| 77 | 4 | 0 |
+--------+-----+---------+

Answer 1

In MySQL you can't select from a table you are deleting from at the same time. But with a temp table you can overcome this problem
DELETE FROM `users_acl`
WHERE userID IN
(
SELECT * FROM
(
SELECT userID
FROM `users_acl`
GROUP BY userID
HAVING COUNT(userID) > 1
AND SUM(`acl` = 4) > 0
) tmp
);
or use a joininstead
DELETE u
FROM `users_acl` u
JOIN
(
SELECT userID
FROM `users_acl`
GROUP BY userID
HAVING COUNT(userID) > 1
AND SUM(`acl` = 4) > 0
) tmp on tmp.userID = u.userID

Answer 2

I think the accepted answer here would actually delete all the duplicates, rather than preserving one unique value.
In case anyone is like me and looking to de-duplicate (rather than delete all duplicates), here's a slightly modified solution:
DELETE u
FROM `users_acl` u
JOIN
(
SELECT COUNT(*), MIN(userID) as min_id, MAX(acl) as value
FROM `users_acl`
WHERE 1
GROUP BY name,value,timestamp,ip HAVING COUNT(*) > 1
) tmp on u.id > tmp.min_id and u.value = tmp.value