排序分组优化
2021-04-09 01:29
标签：group esc 排序 family mysq loading http sql 使用 1.说明 在使用order by时，经常会出现Using fileSort 在使用group by时，使用不当，会出现Using temporay 1..Using fileSort 说明会对数据使用一个外部的索引排序 而不是内部的索引顺序进行 mysql无法利用索引完成排序操作称为文件排序 1.索引使用情况 效果： 结论： 使用覆盖索引，同时order by符合索引顺序。也不能一升一降。 1.说明 分组前必排序 2. 排序分组优化 标签：group esc 排序 family mysq loading http sql 使用 原文地址：https://www.cnblogs.com/juncaoit/p/13376171.html二：排序
explain
select * from employee where name = ‘鲁班‘ and dep_id = 1 order by age;
explain
select name,dep_id,age from employee order by name,dep_id,age;
explain
select * from employee order by name,dep_id,age;
explain
select name,dep_id,age from employee order by name,age;
explain
select * from employee where name = ‘鲁班‘ order by dep_id,age;
explain
select name,dep_id,age from employee where name = ‘鲁班‘ order by dep_id,age;
explain
select name,dep_id,age from employee where name = ‘鲁班‘ and dep_id > 1 order by age;
explain
select name,dep_id,age from employee where name = ‘鲁班‘ order by age,dep_id;
explain
select name,dep_id,age from employee where name = ‘鲁班‘ order by dep_id asc, age desc;
三：分组