[MySQL] 使用force index强制使用索引
1.在测试一个按照时间的范围查询时,尽管增加了索引,发现使用不到索引,可以使用这个来强制使用索引
测试过程为,创建下面的表,以及创建了联合索引
create table delay_delete_users(
id int auto_increment,
email_id int not null default 0 comment 'email表id',
email varchar(50) not null default '' comment '邮箱前缀',
entid int not null default 0 comment '企业id',
default_domain varchar(50) not null default '' comment '默认域',
delete_time timestamp comment '删除时间',
clear tinyint not null default 0 comment '0未处理,1已清空',
primary key (id),
key email_entid(email,entid),
key delete_time(delete_time,clear)
)engine innodb;插入测试数据,进行explain查询
insert into `delay_delete_users` (email,entid,default_domain,delete_time)value('shihan2',23684,'appdev.sinanet.com','2019-12-10 15:49:16');
insert into `delay_delete_users` (email,entid,default_domain,delete_time,clear)value('shihan2',23684,'appdev.sinanet.com','2019-12-10 15:49:16',1);
insert into `delay_delete_users` (email,entid,default_domain,delete_time,clear)value('shihan2',23684,'appdev.sinanet.com','2019-12-12 15:49:16',1);explain select * from delay_delete_users where delete_time<'2019-12-12' and clear=0; 索引没有使用到,还是进行的全表扫描,看那个扫描行数rows
+----+-------------+--------------------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------------------+------------+------+---------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE | delay_delete_users | NULL | ALL | delete_time | NULL | NULL | NULL | 7 | 14.29 | Using where |explain select * from delay_delete_users force index(delete_time) where delete_time<'2019-12-12' and clear=0;使用到了索引
+----+-------------+--------------------+------------+-------+---------------+-------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+--------------------+------------+-------+---------------+-------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | delay_delete_users | NULL | range | delete_time | delete_time | 4 | NULL | 3 | 14.29 | Using index condition |本文参与 腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
原始发表：2019-12-12 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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