[MySQL/MSSQL] 196. Delete Duplicate Emails

목차

문제

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 delete all the duplicate emails, keeping only one unique email with the smallest id. Note that you are supposed to write a DELETE statement and not a SELECT one.

After running your script, the answer shown is the Person table. The driver will first compile and run your piece of code and then show the Person table. The final order of the Person table does not matter.

The query result format is in the following example.

 

Example 1:

Input: 
Person table:
+----+------------------+
| id | email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Output: 
+----+------------------+
| id | email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+
Explanation: john@example.com is repeated two times. We keep the row with the smallest Id = 1.

풀이

-- MySQL

# Please write a DELETE statement and DO NOT write a SELECT statement.
# Write your MySQL query statement below
# 아이디어
# - 동일한 이메일을 갖고있는 이메일을 찾아 id값이 더 큰쪽을 제거
DELETE p1 
    FROM Person as p1
        ,Person as p2 
    WHERE p1.Email = p2.Email 
        AND p1.Id > p2.Id;
        
-- MSSQL

/* 
 Please write a DELETE statement and DO NOT write a SELECT statement.
 Write your T-SQL query statement below
 */
 delete p1
    from Person as p1
        inner join Person as p2
        on p1.email = p2.email
    where p1.id > p2.id