Calculate Date-based Data with PHP and SQL?

I want to know how to calculate Date-based Data with PHP and MySQL.

I need to know how to build the database and how to calculate the time different with PHP.

For example I want to get the order number in special time period.

Please let me know URL if you have a demo in web.

Thanks

I also need know how to compare a time.for example how to write the SQL to get the order between April 3,2002 aand Aug 5,2002.

Thanks a lot.

Assuming your dates are datetime fields in MySQL...

SELECT * FROM table WHERE ( datetime_field > '2003-05-00' AND datetime_field < '2003-05-30' )

Will get you dates between April 30 and May 30... theres other stuff like BETWEEN statements, but that should get you started.