面试题中经常遇到的SQL题：删除重复数据，保留其中一条

    如题，解决思路如下:

    1、首先我们需要找出拥有重复数据的记录

---以name字段分组
select Name,COUNT(Name) as [count] from Permission group by Name-- having COUNT(Name)>1

---以name字段分组，筛选出有重复出现的字段 having 用于条件筛选 作用相当于where 区别where用于group by 之前，having用于之后
select Name,COUNT(Name) as [count] from Permission group by Name having COUNT(Name)>1

    执行结果：

    

   2、然后我们需要知道要要保留的记录的ID号，或者其他唯一标识字段

---获取重复记录中最小的一项的ID号
select min(ID),Name,COUNT(Name) as [count] from Permission group by Name having COUNT(Name)>1

   执行结果：

    

   3、组合前面两个数据查询条件，进行删除操作

---删除重复数据
delete from Permission 
---找出拥有相同数据的记录
where Name in (select Name from Permission group by Name having COUNT(Name)>1)
---除了最小ID号的数据保留，其他的删除 (也可以用max(id))
and ID not in (select min(ID) from Permission group by Name having COUNT(Name)>1)