196. Delete Duplicate Emails

Giới thiệu bài toán

Chi tiết: https://leetcode.com/problems/delete-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.

Yêu cầu

Write a solution to delete all duplicate emails, keeping only one unique email with the smallest id.

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 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.

Giải quyết bài toán

DELETE FROM Person
WHERE id NOT IN (
    SELECT id
    FROM (
        SELECT MIN(p.id) as id FROM Person p
        GROUP BY p.email
    ) AS c
);

Tham khảo: https://leetcode.com/submissions/detail/1039208682/