182_DuplicateEmails.md

182. Duplicate Emails

SQL Schema Table: Person

+-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key column for this table. Each row of this table contains an email. The emails will not contain uppercase letters.

Example 1:

Input: 
Person table:
+----+---------+
| id | email   |
+----+---------+
| 1  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+
Output: 
+---------+
| Email   |
+---------+
| a@b.com |
+---------+
Explanation: a@b.com is repeated two times.

Solution:

• 解法: 找重複的email, 就下意識想使用group by來查詢是否有重複的。

code:

• SQL

select Email from Person
group by Email
having count(*)>1;