关于mysql limit查询优化思路
1. 思路一:先全部走索引(避免其它数据读取,或者此时索引都在内存中),拿到主键,再查一遍
- 场景:
1.二级索引 KEY `ind_wlb_ext_order_item_itemid` (`seller_id`,`item_id`,`status`)
2.seller_id = 2023990209, 有42000条数据 - 执行
– SELECT * FROM wlb_ext_order_item where seller_id = 2023990209 limit 100, 1000; // 0.046ms
– SELECT * FROM wlb_ext_order_item where seller_id = 2023990209 limit 1000, 1000; // 0.063ms
– SELECT * FROM wlb_ext_order_item where seller_id = 2023990209 limit 40000, 1000; // 0.279ms - 优化
– SELECT * from wlb_ext_order_item m, (SELECT id from wlb_ext_order_item where seller_id = 2023990209 limit 40000, 1000) t WHERE m.id = t.id; // 0.062ms
explain查看执行计划:
1.SELECT * FROM wlb_ext_order_item where seller_id = 2023990209 limit 40000, 1000; // 0.279ms
2.SELECT * from wlb_ext_order_item m, (SELECT id from wlb_ext_order_item where seller_id = 2023990209 limit 40000, 1000) t WHERE m.id = t.id; // 0.062ms
2. 思路二:利用主键自身的顺序特性
http://www.fuchaoqun.com/2009/04/efficient-pagination-using-mysql/