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这篇文章主要介绍了mysql查找删除重复数据并只保留一条实例详解的相关资料,需要的朋友可以参考下
有这样一张表，表数据及结果如下：
| school_id |
school_name |
total_student |
test_takers |
| 1239 |
Abraham Lincoln High School |
55 |
50 |
| 1240 |
Abraham Lincoln High School |
70 |
35 |
| 1241 |
Acalanes High School |
120 |
89 |
| 1242 |
Academy Of The Canyons |
30 |
30 |
| 1243 |
Agoura High School |
89 |
40 |
| 1244 |
Agoura High School |
100 |
50 |
我们可以看出，school_name的字段值有重复数据(Abraham Lincoln High School 和Agoura High School分别出现两次)，那么如何删除这两条数据，从而只让这两个数值出现一次呢？ 具体实现方法如下：
1、删除重复记录,保存Id最小的一条
delete FROM `test` WHERE `school_name` in (SELECT `school_name`
FROM `test`
GROUP BY `school_name`
HAVING COUNT( * ) >1) and school_id not in (select min(school_id) from test group by school_id having count(* )>1)
先使用GROUP BY having语法查询出重复的数据，然后删除重复数据并保留school_id最小的一条.
2、删除重复记录,保存Id最大的一条
delete FROM `test` WHERE `school_name` in (SELECT `school_name`
FROM `test`
GROUP BY `school_name`
HAVING COUNT( * ) >1) and school_id not in (select max(school_id) from test group by school_id having count(* )>1)
原理和上面一样。
以上就是mysql查找删除重复数据并只保留一条实例详解，希望能帮助到大家，谢谢大家对本站的支持！ | 
发表于 2018-12-25 17:13:51
