mysql查找删除重复数据并只保留一条

有这样一张表，表数据及结果如下：

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。