Question

i couldn’t find a way to optimize the following Query:

SELECT * 
FROM tbl 
WHERE type='51' AND `start`<='2012-01-19' 
ORDER BY end DESC 
LIMIT 5

I’ve tried by indexing each column in a separate index (type,start,end), and all of them in the same index, but MySQL keeps telling me that needs to do a filesort

Is this query just impossible to optimize?

Answer 1

Yes, as long you have range comparison in WHERE and sort by another field – mysql cannot use index for sorting.

It could if you had WHERE type='51' ANDstart='2012-01-19' ORDER BY end DESC or WHERE type='51' ANDstart<= '2012-01-19' ORDER BY start DESC

http://dev.mysql.com/doc/refman/5.5/en/order-by-optimization.html — and here is a chapter relevant to your problem