MySQL - order by优化初探

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DB Version

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.28    |
+-----------+
1 row in set

mysql> 

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Table

CREATE TABLE `employees` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(24) NOT NULL DEFAULT '' COMMENT '姓名',
  `age` int(11) NOT NULL DEFAULT '0' COMMENT '年龄',
  `position` varchar(20) NOT NULL DEFAULT '' COMMENT '职位',
  `hire_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '入职时间',
  PRIMARY KEY (`id`),
  KEY `idx_name_age_position` (`name`,`age`,`position`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COMMENT='员工记录表';

两个索引

1. 主键索引
2. 二级索引 idx_name_age_position

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数据量

mysql> select count(1) from employees ;
+----------+
| count(1) |
+----------+
|   100002 |
+----------+
1 row in set

mysql> 

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案例一

explain select * from employees where name = 'LiLei' and position = 'dev' order by age ;

先想一下这个order by 会不会走索引 ？