ORDER BY Optimization depends on LIMIT

[Goran Prijic]

Hi,

I have this query

SELECT *
FROM `content` AS `c`
WHERE c.module = 20
AND c.categoryID
IN ('50', '31', '16', '10')
ORDER BY `c`.`released` DESC
LIMIT 5

Table has approximately 500 000 rows but this query should not return any.

This query will execute with ORDER BY optimization when LIMIT is less than 4. When LIMIT is greater than 4, using filesort will be run.

Does anyone know how ORDER BY optimization depends on LIMIT and how this dependency can be changed?



Edited 2 time(s). Last edit at 03/24/2011 08:50AM by Goran Prijic.