【MySQL】记一次数据去重

雨点打透心脏的1/2处 2022-06-10 12:51 190阅读 0赞

有时候，因为开发时，考虑不当，会造成数据重复。

背景：

前几天做项目的时候，有一个给ip打标签的操作，但是当数据数量多了以后，发现，同一个ip被打了两次相同的标签，导致数据显示重复，然而，已经使用了一段时间了，只能在原有数据库上删除重复数据，然后修改添加标签的逻辑了，去重操作如下：

mysql> select * from vip_port_tag;
    +-------+----------------+-------+-------------------+
    | id    | vip            | port  | tag               |
    +-------+----------------+-------+-------------------+
    | 32446 | 10.172.95.38   | 19527 | ttttttttttttttttt |
    | 32447 | 111.206.52.82  |    80 | ttttttttttttttttt |
    | 32448 | 221.181.72.212 |   443 | ttttttttttttttttt |
    | 32449 | 182.118.31.28  |  2229 | ttttttttttttttttt |
    | 32450 | 10.172.95.38   | 19527 | ttttttttttttttttt |
    | 32451 | 111.206.52.82  |    80 | ttttttttttttttttt |
    +-------+----------------+-------+-------------------+
    6 rows in set
    
    mysql>

可以很明显的看到，vip为10.172.95.38,port为19527还有vip为111.206.52.82，port为90的被连续两次打了相同的标签。

去重思想，根据同一tag，还有vip，port，分组，然后统计每组的个数，大于1的，即为有重复的。

mysql> select id,count(*) as cnt,tag,vip,port from vip_port_tag group by tag,vip,port;
    +-------+-----+-------------------+----------------+-------+
    | id    | cnt | tag               | vip            | port  |
    +-------+-----+-------------------+----------------+-------+
    | 32446 |   2 | ttttttttttttttttt | 10.172.95.38   | 19527 |
    | 32447 |   2 | ttttttttttttttttt | 111.206.52.82  |    80 |
    | 32449 |   1 | ttttttttttttttttt | 182.118.31.28  |  2229 |
    | 32448 |   1 | ttttttttttttttttt | 221.181.72.212 |   443 |
    +-------+-----+-------------------+----------------+-------+
    4 rows in set

cnt那一列，大于1的就为重复列

mysql> select id,count(*) as cnt,tag,vip,port from vip_port_tag where id>32445 group by tag,vip,port having cnt>1;
    +-------+-----+-------------------+---------------+-------+
    | id    | cnt | tag               | vip           | port  |
    +-------+-----+-------------------+---------------+-------+
    | 32446 |   2 | ttttttttttttttttt | 10.172.95.38  | 19527 |
    | 32447 |   2 | ttttttttttttttttt | 111.206.52.82 |    80 |
    +-------+-----+-------------------+---------------+-------+
    2 rows in set

检验

mysql> select * from vip_port_tag where vip="10.172.95.38" and port="19527";
    +-------+--------------+-------+-------------------+
    | id    | vip          | port  | tag               |
    +-------+--------------+-------+-------------------+
    | 32446 | 10.172.95.38 | 19527 | ttttttttttttttttt |
    | 32450 | 10.172.95.38 | 19527 | ttttttttttttttttt |
    +-------+--------------+-------+-------------------+
    3 rows in set

然后就可以考虑删除哪一项，比如保留id较小的那个，则选出id最大的那一项

mysql> select max(id) as id,count(*) as cnt,tag,vip,port from vip_port_tag where id>32445 group by tag,vip,port having cnt>1;
    +-------+-----+-------------------+---------------+-------+
    | id    | cnt | tag               | vip           | port  |
    +-------+-----+-------------------+---------------+-------+
    | 32450 |   2 | ttttttttttttttttt | 10.172.95.38  | 19527 |
    | 32451 |   2 | ttttttttttttttttt | 111.206.52.82 |    80 |
    +-------+-----+-------------------+---------------+-------+
    2 rows in set

然后根据id执行删除操作即可

mysql> delete from vip_port_tag where id in (select id from (select max(id) as id,count(*) as cnt,tag,vip,port from vip_port_tag group by tag,vip,port having cnt>1) as t);
    Query OK, 2 rows affected

再查看原数据

mysql> select * from vip_port_tag;
    +-------+----------------+-------+-------------------+
    | id    | vip            | port  | tag               |
    +-------+----------------+-------+-------------------+
    | 32446 | 10.172.95.38   | 19527 | ttttttttttttttttt |
    | 32447 | 111.206.52.82  |    80 | ttttttttttttttttt |
    | 32448 | 221.181.72.212 |   443 | ttttttttttttttttt |
    | 32449 | 182.118.31.28  |  2229 | ttttttttttttttttt |
    +-------+----------------+-------+-------------------+
    4 rows in set

OK，重复数据，就这么被干掉了。

知识点总结

*  group by语句，可以为多个字段
 *  having 选出符合条件的分组
 *  count 统计分组个数
 *  max 选出分组中id最大的那个
 *  临时表