背景
近期在做用户标签项目，目前标签的存储是用户id，标签ids（每个标签以,形式存储） 的形式，但是如果想统计前后两天标签的变化，使用find_in_set函数，一方面查询速度慢（因为不能使用索引），另一方面目前标签已有将近300多个，以后还会更多，一个标签一个标签的写，使得sql特别长。
目前采取的策略是：将用户标签表拆分成 用户id，标签id的形式。这样将前后两天的表关联，就能查出昨天到今天有那些标签离开，哪些标签进来。
那么采用上述策略就需要研究怎么将用户id，标签ids的形式转换成用户id，标签id的形式。
探索
我们知道像 1,2,3,4,5,212 这种字符串，如果要分别取到1 2 3 4 5 212，用编程的思想就是先将该字符串用","分隔成一个数据，然后遍历取到数组里的每一个值，但是在mysql里并没有数组的概念，但是我们可以用各种方法求得字符串的长度，以及求得使用“,”分隔后有多少个值。也可以用mysql可以采取的字符串截取的形式去获得相应位置的数值。下面就让我们看一下吧~
实现
- 相关表结构
CREATE TABLE `tagids_label` (
`userid` int(11) NOT NULL COMMENT '用户id',
`label` int(11) NOT NULL COMMENT '标记，暂时 保留三天的数据，day%3 ',
`day` int(11) NOT NULL COMMENT '对应的统计日期的天',
`tagids` text NOT NULL COMMENT '标签id，以，（英文）分隔',
`createTime` datetime NOT NULL COMMENT '创建时间',
`updateTime` datetime NOT NULL COMMENT '更新时间',
PRIMARY KEY (`userid`,`label`),
KEY `index_day` (`day`),
KEY `index_label` (`label`),
KEY `index_label_userid` (`userid`,`label`),
KEY `index_createTime_userid` (`userid`,`createTime`),
KEY `index_userid` (`userid`),
KEY `index_createtime` (`createTime`) USING BTREE,
FULLTEXT KEY `index_tagids` (`tagids`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='用户标签结果表'
CREATE TABLE `sequence` (
`seq` int(3) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
ps:sequence表表示标签的个数，从1到最大个数
-
获得固定分隔符分隔后元素个数
- 原数据
SELECT * FROM `tagids_label` WHERE `userid` =2blockchain171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227- 分隔符分隔后元素个数
SELECT length(`tagids`) ,length(REPLACE (`tagids`,',','')),length(`tagids`)-length(REPLACE (`tagids`,',',''))+1 FROM `tagids_label` WHERE `userid` =2image.png- 注：length(
tagids)计算字符串长度，以字节为单位，每个数字、英文标点符号是一个字节，每个中文、中文标点符号是3个字节。length(tagids)表示tagids含有多少个数字和标点符号
replace(tagids,',','')将字符串tagids里的","用空字符来代替，length(replace(tagids,',',''))就表示tagids含有多少个数字。
length(tagids)-length(replace(tagids,',','')) 表示tagsid含有多少个标点符号，那标点符号+1就表示tagids用","分隔符分隔后含有多少个元素，即标签个数。
- substring_index 截取字符串
- 根据关键字","截取字符串
结果：SELECT substring_index('171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227', ',',1) UNION ALL SELECT substring_index('171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227', ',',2) UNION ALL SELECT substring_index('171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227', ',',3) UNION ALL SELECT substring_index('171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227', ',',4) UNION ALL ...... UNION ALL SELECT substring_index('171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227',',',61)171 171,172 171,172,173 171,172,173,174 ...... 171,172,173,174,175,184,187,189,191,192,49,52,55,90,96,101,104,110,7,9,253,270,277,280,129,131,134,136,138,139,231,241,58,63,66,70,72,75,77,79,84,149,150,159,163,165,166,193,195,256,225,236,246,248,197,200,207,221,210,278,227- 注：substring_index（str,delim,count） 说明：substring_index（被截取字段，关键字，关键字出现的次数），如果count=-1我们就可以截取到倒数第一个被关键字分隔的元素。只要在上面查询结果中再使用一次substring_index即可获得每个被关键字分隔的元素。
- 最终实现
SELECT
userid,
SUBSTRING_INDEX(
SUBSTRING_INDEX(tagids, ',', seq),
',' ,- 1
) sub_id,
seq
FROM sequence
JOIN (SELECT * FROM `tagids_label` WHERE userid = 2)b
WHERE
seq BETWEEN 1
AND (
SELECT
1 + LENGTH(tagids) - LENGTH(replace(tagids, ',', ''))
)
ORDER BY
userid,
tagids;
-
结果：
image.png
image.png
