《PHP实战：mysql查找删除重复数据并只保留一条实例详解》要点：
本文介绍了PHP实战：mysql查找删除重复数据并只保留一条实例详解，希望对您有用。如果有疑问，可以联系我们。
有这样一张表,表数据及结果如下：PHP实战
| 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：PHP实战
1、删除重复记录,保存Id最小的一条PHP实战
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.PHP实战
2、删除重复记录,保存Id最大的一条PHP实战
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.PHP实战
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!PHP实战
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