Delete Duplicate Emails

原题leetcode,数据库常用操作去重，思路就是按照email列相同合并后（其实这时候已经去重了）取出ID，从person中删除不存在ID

# Select 嵌套使用临时表时，需要为临时表指定别名 a。
# group 默认不会选择最大最小ID，只会选择行靠前的ID
delete 
from person 
where Id not in 
(select * from (select min(Id) from person group by Email)as a)

DELETE p from Person p, Person q where p.Id>q.Id AND q.Email=p.Email