Use Case of HAVING() in SQL leetcode question

 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.

 

Write an SQL query to report all the duplicate emails.

Return the result table in any order.

The query 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.

Solution :

# Write your MySQL query statement below

select Email

from Person

group by Email

having count(Email) > 1;

Approach :

First Approach is finding out count of each email address

1)

# Write your MySQL query statement below

select Email, count(Email)

from Person

group by Email

After getting count of emails we will further modify the code as below by using HAVING( ) and we will filter out emails with count more than 2.

select Email

from Person

group by Email

having count(Email) > 1;