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LeetCode-14.database

十四、database

优先顺序:where>group by>having>order by

182. 查找重复的电子邮箱

链接:https://leetcode-cn.com/problems/duplicate-emails/

SQL架构
编写一个 SQL 查询,查找 Person 表中所有重复的电子邮箱。

示例:

+----+---------+
| Id | Email   |
+----+---------+
| 1  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+
根据以上输入,你的查询应返回以下结果:

+---------+
| Email   |
+---------+
| a@b.com |
+---------+
说明:所有电子邮箱都是小写字母。
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# Write your MySQL query statement below
# 1.使用group by 和临时表
select Email from
(
select Email, count(Email) as nums
from Person
group by Email
) as tmp
where nums>1;
# 2.使用group by和having条件
select Email
from Person
group by Email
having count(Email) > 1;
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