-- key_value is the name of the column in the original_table table in my database.

SELECT DISTINCT *
      INTO duplicate_table
      FROM original_table
      GROUP BY key_value
      HAVING COUNT(key_value) > 1

   DELETE original_table
      WHERE key_value
      IN (SELECT key_value
             FROM duplicate_table)

   INSERT original_table
      SELECT *
         FROM duplicate_table

     DROP TABLE duplicate_table