對於分割槽字段必須是主鍵的一部分，那麼建了復合主鍵之後，是否需要對分許字段再單獨新增乙個索引呢？有沒有效果？下面來驗證一下
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);
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 ('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');
explain partitions
select * from effect_new_index
where create_time = '2017-10-14 12:00:00'
idselect_type
table
partitions
tpye
possible_keys
keykey_len
refrows
filtered
extra
1******
effect_new
p8all
null
null
null
null
391515
10using where
結果為：
idselect_type
table
partitions
tpye
possible_keys
keykey_len
refrows
filtered
extra
1******
effect_new
p8ref
idx_ctime
idx_ctime
5const
60760
100null
雖然表已經根據此欄位分割槽，但這不能等同於索引。分了區，只能說該字段為某個值的記錄會在某個分割槽裡面，但不是索引，還要一頓好找。
有時候，主鍵不等於分割槽依據列，這時候主鍵又想建聚集索引的話，那麼必須包含分割槽依據列，搞成復合主鍵。那麼，這種情況下，分割槽依據列不就有索引了嗎？是的，可是它不夠快，如果在這個復合索引裡面，分割槽依據列不排在第一位，就不夠快，如果查詢語句裡常常用分割槽依據列作為過濾條件，就有必要為分割槽依據列額外單獨建立乙個索引。
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