sql datetime comparison in where clause code example

Example: compare date in sql

WHERE DATEDIFF(my_date,'2008-11-20') >=0;
WHERE my_date >= '2008-11-20';
WHERE to_date(my_date, 'YYYY-MM-DD') >= '2008-11-20';
WHERE to_date(my_date, 'YYYY-MM-DD') >= to_date('2008-11-20', 'YYYY-MM-DD');