When you are working with SQL and MySQL then its developer responsibility to make the perfect database structure and data. now if you have database and there is some redundant data in that database and you need to remove the redundant data from the table then you can do it using one SQL statement.
you can remove the duplicate data using Below SQL statement
DELETE FROM Tablename USING Tablename, Tablename as VirtualTable WHERE (NOT Tablename.ID=VirtualTable.ID) AND (Tablename.Fieldname=VirtualTable.Fieldname)
Above SQL Statement is used to delete duplicate rows in table.
In the SQL Statement you need to alter the Tablename and Fieldname as per your Database