MySQL分区字段列有必要再单独建索引吗?
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2022-04-03 20:25:05
前言
大家都知道对于分区字段必须是主键的一部分,那么建了复合主键之后,是否需要对分许字段再单独添加一个索引呢?有没有效果?来验证一下,下面话不多说了,来一起看看详细的介绍...
前言
大家都知道对于分区字段必须是主键的一部分,那么建了复合主键之后,是否需要对分许字段再单独添加一个索引呢?有没有效果?来验证一下,下面话不多说了,来一起看看详细的介绍吧。
1、新建表effect_new(以创建时间按月分区)
create table `effect_new` ( `id` bigint(20) not null auto_increment, `type` tinyint(4) not null default '0', `timezone` varchar(10) default null, `date` varchar(10) not null, `hour` varchar(2) default null, `position` varchar(200) default null, `country` varchar(32) not null, `create_time` datetime not null default '1970-01-01 00:00:00', primary key (`id`,`create_time`), key `index_date_hour_coun` (`date`,`hour`,`country`) ) engine=innodb auto_increment=983041 default charset=utf8 partition by range (to_days (`create_time`)) (partition p0 values less than (736754) engine = innodb, partition p1 values less than (736785) engine = innodb, partition p2 values less than (736815) engine = innodb, partition p3 values less than (736846) engine = innodb, partition p4 values less than (736876) engine = innodb, partition p5 values less than (736907) engine = innodb, partition p6 values less than (736938) engine = innodb, partition p7 values less than (736968) engine = innodb, partition p8 values less than (736999) engine = innodb, partition p9 values less than (737029) engine = innodb, partition p10 values less than (737060) engine = innodb);
2、插入部分数据数据,
insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('1', '0', 'gmt+8', '2017-07-01', '', 'm-noticleanfull-familyrecom-0026', '', '2017-07-02 00:07:02'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('2', '1', 'gmt+8', '2017-09-30', '23', 'ma5dtjub', 'eg', '2017-10-01 00:00:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('3', '1', 'gmt+8', '2017-09-10', '10', '28', 'dz', '2017-09-11 00:08:20'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('4', '1', 'gmt+8', '2017-02-03', '20', '32', 'ad', '2017-02-04 00:00:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('5', '0', 'gmt+8', '2017-03-05', '2', null, 'ai', '2017-03-06 02:10:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('6', '0', 'gmt+8', '2017-09-23', '13', 'm-brandsplash-s-0038', 'ag', '2017-09-23 13:00:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('7', '1', null, '2017-10-13', '12', 'bb-main-appad-0018', 'af', '2017-10-14 12:00:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('8', '0', 'gmt+8', '2017-10-28', '2', 'm-chargereminder-s-0040', 'ae', '2017-10-29 00:00:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('9', '1', 'gmt+8', '2017-10-09', null, '30', 'ai', '2017-10-10 00:09:00'); insert into `effect_new` (`id`, `type`, `timezone`, `date`, `hour`, `position`, `country`, `create_time`) values ('10', '0', 'gmt+8', '2017-10-05', '5', ' m-brandsplash', 'la', '2017-10-06 05:10:00');
3、分析语句
explain partitions select * from effect_new_index where create_time = '2017-10-14 12:00:00'
结果为:
id | select_type | table | partitions | tpye | possible_keys | key | key_len | ref | rows | filtered | extra |
1 | simple | effect_new | p8 | all | null | null | null | null | 391515 | 10 | using where |
4、给表effect_new添加索引idx_ctime
5、分析添加索引后的执行计划
结果为:
id | select_type | table | partitions | tpye | possible_keys | key | key_len | ref | rows | filtered | extra |
1 | simple | effect_new | p8 | ref | idx_ctime | idx_ctime | 5 | const | 60760 | 100 | null |
6、结论:
虽然表已经根据此字段分区,但这不能等同于索引。分了区,只能说该字段为某个值的记录会在某个分区里面,但不是索引,还要一顿好找。
有时候,主键不等于分区依据列,这时候主键又想建聚集索引的话,那么必须包含分区依据列,搞成复合主键。那么,这种情况下,分区依据列不就有索引了吗?是的,可是它不够快,如果在这个复合索引里面,分区依据列不排在第一位,就不够快,如果查找语句里常常用分区依据列作为过滤条件,就有必要为分区依据列额外单独建立一个索引。
总结
以上就是这篇文章的全部内容了,本文还有许多不足,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,如果有疑问大家可以留言交流,谢谢大家对的支持。
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