查找重复的值

 表Person

找出重复的email的值

思路1：两表查询，distinct去重

select distinct a.Email

from Person a,Person b

where a.id <>b.id and a.Email = b.Email

思路2：group by 分组，having 过滤，sum()函数计数>1

select Email

from Person 

group by Email

having sum(Email)>1