Have you ever seen index which refused to be used even if there is every reason for it to work (from the glance view): mysql> explain select * from article where article_id=10; +—-+————-+———+——+—————+——+———+——+——-+————-+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +—-+————-+———+——+—————+——+———+——+——-+————-+ [...]