SqlServer 删除表中重复数据

-- 第一步 根据一个或多个关键字段, 找出表中重复数据

-- 单个字段
select username,count(1) from sysUser group by username having count(username) > 1

-- 多个字段
select username,userSchool,count(1) from sysUser group by username,userSchool having count(username) > 1  and count(userSchool) >1

-- 第二步 找出重复数据中的ID最大值或ID最小值

select min(id) from sysUser group by username having count(username) > 1

-- 第三步 删除重复数据

delete from sysUser where
username in
(select username from sysUser group by username having count(username) > 1)
and id not in 
( select min(id) from sysUser group by username having count(username) > 1)