SQL : delete duplicate rows except one

delete.sql

DELETE FROM myTable
WHERE (col1, col2, col2, col3)
IN (
  SELECT * FROM (
     SELECT  col1, col2, col2, col3
     FROM myTable
     GROUP BY col1, col2, col2, col3
     HAVING count(*) > 1
     ) AS T
     -- remove this where condition if you want to delete all duplicate rows
     WHERE id NOT IN (	
        SELECT * FROM (
           SELECT id
           FROM  myTable
           GROUP BY col1, col2, col2, col3
           HAVING count(*) > 1
        ) AS T
     )
);