182. Duplicate Emails
SQL架构
Create table If Not Exists Person (Id int, Email varchar(255))
Truncate table Person
insert into Person (Id, Email) values ('1', 'a@b.com')
insert into Person (Id, Email) values ('2', 'c@d.com')
insert into Person (Id, Email) values ('3', 'a@b.com')Write a SQL query to find all duplicate emails in a table named Person.
Example:
| Id | |
|---|---|
| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
For example, your query should return the following for the above table:
| a@b.com |
Note: All emails are in lowercase.
解题思路：
使用 GROUP BY 和 HAVING 条件：向 GROUP BY 添加条件的一种更常用的方法是使用 HAVING 子句，该子句更为简单高效。
GROUP BY 语句用于结合合计函数，根据一个或多个列对结果集进行分组。
解答：
select Email from Person
group by Email having count(Email) > 1;
