如何进行SQL优化中的limit分页优化

如何进行SQL优化中的limit分页优化，相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

示例

表aaaaa中共有2375690数据。

优化前的SQL

SQL执行结果：

SELECT DISTINCT(device_id) uid FROM aaaaa WHERE status = 0 LIMIT 88000,1000;1000 rows in set (0.48 sec)

SQL执行计划：

MariaDB [star]> explain SELECT sql_no_cache DISTINCT(device_id) uid FROM aaaaa WHERE status = 0 LIMIT 88000,1000;+------+-------------+---------------+------+---------------+------+---------+------+---------+------------------------------+| id   | select_type | table         | type | possible_keys | key  | key_len | ref  | rows    | Extra                        |+------+-------------+---------------+------+---------------+------+---------+------+---------+------------------------------+|    1 | SIMPLE      | aaaaa         | ALL  | NULL          | NULL | NULL    | NULL | 2375690 | Using where; Using temporary |+------+-------------+---------------+------+---------------+------+---------+------+---------+------------------------------+

优化方式

迅速定位起始ID，利用主键索引，加快扫描速度。可以看到，derived中，SQL使用到了覆盖索引进行扫描，虽然还是全表扫，因为只扫描id列，大大降低了扫描的IO耗费，快速定位到了id。

MariaDB [star]> explain SELECT sql_no_cache DISTINCT(device_id) uid FROM aaaaa join (select id from aaaaa limit 88000,1) k on star_device_5.id>=k.id where status=0 limit 1000; +------+-------------+---------------+-------+---------------+-------------+---------+------+---------+------------------------------------------------+| id   | select_type | table         | type  | possible_keys | key         | key_len | ref  | rows    | Extra                                          |+------+-------------+---------------+-------+---------------+-------------+---------+------+---------+------------------------------------------------+|    1 | PRIMARY     |     | ALL   | NULL          | NULL        | NULL    | NULL |   88001 | Using temporary                                ||    1 | PRIMARY     | star_device_5 | ALL   | PRIMARY       | NULL        | NULL    | NULL | 2377112 | Range checked for each record (index map: 0x1) ||    2 | DERIVED     | star_device_5 | index | NULL          | idx_star_id | 8       | NULL | 2377112 | Using index                                    |+------+-------------+---------------+-------+---------------+-------------+---------+------+---------+------------------------------------------------+

执行结果：

SELECT sql_no_cache DISTINCT(device_id) uid FROM star_device_5 join (select id from star_device_5 limit 880000,1) k on star_device_5.id>=k.id where status=0 limit 1000;1000 rows in set (0.19 sec)

随着m的增大和n的增大，两种写法的SQL执行时间会有本质差别。我做了测试，当m值增加到880000时，优化前的SQL需要2分钟，优化后的SQL还是0.1s左右。

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