select Email from (
select Email, count(Email) as num from Person
group by Email )
as result
where num>1
select Email, count(Email) as num from Person group by Email
#创建一个辅助表，并使用Email 内容对其进行归类存储
select Email from 辅助表 as result where num>1
#条件查询获取重复项
参考：https://leetcode-cn.com/problems/duplicate-emails/solution/cha-zhao-zhong-fu-de-dian-zi-you-xiang-by-leetcode/