Below are some methods of comparing dates in MYSQL.
Finding rows entered in the last 6 months with MYSQL.
WHERE post_date > DATE_SUB(GETDATE(), INTERVAL 6 MONTH)
Finding the number of days between two dates
SELECT DATEDIFF(end_date ,start_date)
Finding the midpoint or average between to dates.
SELECT (start_date+INTERVAL DATEDIFF(end_date ,start_date)/2 DAY)