1) Make sure it uses index It is very important to have ORDER BY with LIMIT executed without scanning and sorting full result set, so it is important for it to use index
For example if I do SELECT * FROM sites ORDER BY date_created DESC LIMIT 10; I would use index on (date_created) to get result set very fast.
2) Now what if I have something like SELECT * FROM sites WHERE category_id=5 ORDER BY date_created DESC LIMIT 10;
In this case index by date_created may also work but it might not be the most efficient – If it is rare category large portion of table may be scanned to find 10 rows. So index on (category_id, date_created) will be better idea.
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