SQL语句优化
IN语句的优化
demo 1
慢语句
SELECT * FROM t_user WHERE id IN(SELECT MAX(id) FROM t_user GROUP BY country)
优化
SELECT * FROM t_user t1, (SELECT MAX(id) AS id FROM t_user GROUP BY country) t2 WHERE t1.id = t2.id
大表查询优化
随着数据库数据的增加，查询速度会越来越慢，可以开启log_slow_queries慢查询日志，通过查看慢查询日志找到慢语句，进行优化。