21-00182-duplicate-emails.sql

-- 182. Duplicate Emails
Table: Person

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

Write a solution to report all the duplicate emails. Note that it's guaranteed that the email field is not NULL.

Return the result table in any order.

The result format is in the following example.

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.

-- SQL Schema
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')

-- Solution

-- use group by for aggregate

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


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