LEETCODE 196 - Delete Duplicate Emails - Solution in MySQL | LEETCODE 196 Database SQL Solution

LEETCODE | 196

Delete Duplicate Emails

LEETCODE 196 - Delete Duplicate Emails - Solution in MySQL | LEETCODE 196 Database SQL Solution :

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  | [email protected] |
| 2  | [email protected]  |
| 3  | [email protected] |
+----+------------------+
Output: 
+----+------------------+
| id | email            |
+----+------------------+
| 1  | [email protected] |
| 2  | [email protected]  |
+----+------------------+
Explanation: [email protected] is repeated two times. We keep the row with the smallest Id = 1.

Solution of LEETCODE 196 - Delete Duplicate Emails in MySQL:

DELETE FROM Person WHERE Id NOT IN 

(SELECT * FROM(

    SELECT MIN(Id) FROM Person GROUP BY Email) as p);

or,

delete A from Person A, Person B 

where A.id > B.id and A.email=B.email;

Here, A represent the email you want to delete and A.id > B.id means the id with the greater count should be deleted and A.email=B.email means if both the email is same.

Comment if you find the explanation easy!

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