mysql remove rows when one column is duplicate code example

Example 1: mysql delete duplicate rows but keep one

DELETE c1 FROM contacts c1
INNER JOIN contacts c2 
WHERE
    c1.id > c2.id AND 
    c1.email = c2.email;

Example 2: mysql remove duplicates

DELETE FROM table_name WHERE id 
       NOT IN ( SELECT id FROM table_name 
                   GROUP BY field_1, field_2)