记一次mysql 调优

 SELECT *        FROM tb_qa a LEFT OUTER JOIN tb_account b        ON a.author_id = b.id        ORDER BY a.id DESC        LIMIT 0,10

=>

select *        from ( select *        from tb_qa        order by id desc        limit 0,10)a        left outer join tb_account b        on a.author_id = b.id

重点是外连接加上排序倒序