php3 MySQL------ is it necessary to convert all dates if I want to calculate ?

hello everybody, maybe someone had the same problem before. Is it necessary to convert all dates first from dd/mm/yy to yy/mm/dd and again in MySQL from yy-mm-dd to a number (see example below), if i want to calculate? mysql> select TO_DAYS(9505); -> 733364 mysql> select TO_DAYS('1997-10-07); -> 729669 What I´m looking for is a function, that selects the arrival-date and departure-date from a database and calculates automatically the days between. Thanks for your help in advance and have a nice week, best regards joachim.