oj-sql

题目

182. 查找重复的电子邮箱

考察点

1. groupby，having条件
2. 子查询count

solution

使用group by having

select email as `Email`
from Person
group by email
having count(email)>1;

使用子查询count

select t.email as `Email`
from (
    select email,count( email) as cnt
    from Person
    group by email
) t
where t.cnt>1;