[LeetCode][MySQL] 182. Duplicate Emails

Easy 🔗182. Duplicate Emails

📝문제 요약

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.

✏️문제 풀이

SELECT

SELECT email AS Email

• Email : email 컬럼의 별칭

FROM

FROM Person

• Person 테이블의 데이터를 가져옴

GROUP BY

GROUP BY email

• email 컬럼을 기준으로 그룹화

HAVING

HAVING COUNT(email) > 1

• COUNT(email) > 1 : 그룹화된 이메일의 개수가 2개 이상인 경우만 필터링

💯제출 코드

SELECT email AS Email
FROM Person
GROUP BY email
HAVING COUNT(email) > 1