mysql 两表联查分页排序效率优化

Posted 2020-07-06 蕙芷兰馨

数据库中有两张表

t1 存储消息信息

+-----------+------------------+------+-----+---------+----------------+
| Field     | Type             | Null | Key | Default | Extra          |
+-----------+------------------+------+-----+---------+----------------+
| id        | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| code | int(10) unsigned | NO   | MUL | NULL    |                |
| detail    | varchar(200)     | NO   |     | NULL    |                |
| object    | varchar(50)      | NO   |     | NULL    |                |
| create_at | datetime         | NO   |     | NULL    |                |
+-----------+------------------+------+-----+---------+----------------+

t2 存储消息类型

+--------------+---------------------+------+-----+---------+----------------+
| Field        | Type                | Null | Key | Default | Extra          |
+--------------+---------------------+------+-----+---------+----------------+
| code    | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| level        | tinyint(3) unsigned | NO   | MUL | NULL    |                |
| type         | varchar(30)         | NO   |     | NULL    |                |
| content      | varchar(50)         | NO   |     | NULL    |                |
| status       | tinyint(3) unsigned | NO   |     | NULL    |                |
+--------------+---------------------+------+-----+---------+----------------+

现在需要对这两张表进行分页排序联查。

t1 的记录数 230万条，t2表200条

写了三种查询语句如下：

1）最慢
select t1.*, t2.* from t1, t2 where t1.code = t2.code order by t1.create_at desc limit 1065701,20;
耗时：14.48秒

2）使用left join
SELECT t1.*,t2.level AS level, t2.content AS content FROM t1left join t2on t1.code=t2.code order by create_at desc limit 1065701,20;
耗时：9.71秒

3）先查缩小t1表中的范围，再和t2表进行联查
select t1.*, t2.level AS level, t2.content AS content FROM t1 left join t2 on t1.code=t2.code join (select a.id from t1 a join (SELECT id from t1 order by create_at desc limit 1065721,20) b where a.id = b.id) t where t.id=t1.id;
耗时：1.41秒

总结：

在多表联查分页排序，最大的瓶颈在排序，因此我们应该最大化的优化排序。鉴于此，我们先在t1表中分页排序查出符合条件的id，然后使用这个结果集去查t1、并与t2进行联查获取所有需要的信息。

不知道还有没有更好的优化方式，还请大牛指导：）