196. Delete Duplicate Emails

Delete Duplicate Emails

Problem Description

SQL Schema

    Create table If Not Exists Person (Id int, Email varchar(255))

    Truncate table Person

    insert into Person (id, email) values ('1', 'john@example.com')

    insert into Person (id, email) values ('2', 'bob@example.com')

    insert into Person (id, email) values ('3', 'john@example.com')

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  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.

Approach 1) Join

DELETE p1 FROM Person p1, Person p2 WHERE p1.Email = p2.Email AND p1.Id > p2.Id;

Approach 2) Subquery + Not In

DELETE FROM Person where id not in ( SELECT * FROM (SELECT Min(ID) from person group by email) t);

Approach 3) Subquery + IN

DELETE FROM PERSON WHERE ID IN (
 SELECT ID FROM (SELECT ID, ROW_NUMBER() OVER (PARTITION BY EMAIL ORDER BY ID) NUM_ROW FROM PERSON) T WHERE NUM_ROW!=1)

Conclusion

That’s all folks! In this post, we solved LeetCode problem 196. Delete Duplicate Emails

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