Find and remove duplicate rows by two columns

Question

I read all the relevant duplicated questions/answers and I found this to be the most relevant answer:

INSERT IGNORE INTO temp(MAILING_ID,REPORT_ID) 
SELECT DISTI         


        

Answer 1

This works perfectly in any version of MySQL including 5.7+. It also handles the error You can't specify target table 'my_table' for update in FROM clause by using a double-nested subquery. It only deletes ONE duplicate row (the later one) so if you have 3 or more duplicates, you can run the query multiple times. It never deletes unique rows.

DELETE FROM my_table
WHERE id IN (
  SELECT calc_id FROM (
    SELECT MAX(id) AS calc_id
    FROM my_table
    GROUP BY identField1, identField2
    HAVING COUNT(id) > 1
  ) temp
)

I needed this query because I wanted to add a UNIQUE index on two columns but there were some duplicate rows that I needed to discard first.