How to Remove Duplicate Email Addresses in MySQL While Keeping the Most Recent Record?

MySQL: Deleting Duplicate Records While Retaining the Most Recent

Question: How can I eliminate duplicate email addresses in a MySQL table while preserving the most recent one based on the unique ID field?

Solution:

To achieve this, follow these steps:

1. Identify Duplicate Emails:

   • Retrieve a list of all duplicate email addresses using the query:

     SELECT email
     FROM test
     GROUP BY email
     HAVING COUNT(*) > 1;

2. Find the Latest ID for Each Duplicate:

   • Determine the latest ID associated with each duplicate email using the query:

     SELECT MAX(id) AS lastID, email
     FROM test
     WHERE email IN (
       SELECT email
       FROM test
       GROUP BY email
       HAVING COUNT(*) > 1
     )
     GROUP BY email;

3. Delete Oldest Duplicates:

   • Perform a DELETE operation to remove duplicate emails with an ID less than the latest one:

     DELETE test
     FROM test
     INNER JOIN (
       SELECT MAX(id) AS lastID, email
       FROM test
       WHERE email IN (
         SELECT email
         FROM test
         GROUP BY email
         HAVING COUNT(*) > 1
       )
       GROUP BY email
     ) duplic ON duplic.email = test.email
     WHERE test.id < duplic.lastID;

Optimized Version:

The following optimized version provides the same result while potentially improving performance:

DELETE test
FROM test
INNER JOIN (
  SELECT MAX(id) AS lastID, email
  FROM test
  GROUP BY email
  HAVING COUNT(*) > 1) duplic ON duplic.email = test.email
WHERE test.id < duplic.lastID;

This revised DELETE statement focuses on eliminating the oldest duplicates.

Additional Option:

Alternatively, you can utilize this query provided by Rene Limon:

DELETE FROM test
WHERE id NOT IN (
  SELECT MAX(id)
  FROM test
  GROUP BY email);

This approach retains the most recent duplicate email address based on the maximum ID.

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