MYSQL
(quick guide & examples)
DATEDIFF WILL ROUND UP, LESS THAN 24 HRS COUNT AS 1 DAY. SELECT DATEDIFF(`DATE-A`, `DATE-B`) FROM `TABLE`
TIMESTAMPDIFF WILL NOT ROUND UP, LESS THAN 24 HRS COUNT AS 0. SELECT TIMESTAMPDIFF(DAY, `DATE-A`, `DATE-B`) FROM `TABLE`
SIMPLY SET THE UNIT FOR TIMESTAMPDIFF SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, YEAR SELECT TIMESTAMPDIFF(UNIT, `DATE-A`, `DATE-B`) FROM `TABLE`
MANUAL CALCULATE HOURS TIMESTAMPDIFF(MINUTE, `DATE-A`, `DATE-B`) / 60
TO ROUND UP, DOWN, OFF CEIL(TIMESTAMPDIFF(MINUTE, `DATE-A`, `DATE-B`) / 60) FLOOR(TIMESTAMPDIFF(MINUTE, `DATE-A`, `DATE-B`) / 60) ROUND(TIMESTAMPDIFF(MINUTE, `DATE-A`, `DATE-B`) / 60)
AGE IN DAYS DATEDIFF(NOW(), `DATE-FIELD`)
AGE IN OTHER UNITS TIMESTAMPDIFF(UNIT, NOW(), `DATE-FIELD`)
ADD TO DATE DATE_ADD(`DATE-FIELD`, INTERVAL 7 DAY)
MINUS FROM DATE DATE_SUB(`DATE-FIELD`, INTERVAL 3 DAY)