文章目录
DB Version
mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.28 |
+-----------+
1 row in set
mysql>
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
- 主键索引
- 二级索引 idx_name_age_position
数据量
mysql> select count(1) from employees ;
+----------+
| count(1) |
+----------+
| 100002 |
+----------+
1 row in set
mysql>
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 ?