you can convert a date time into a bazillion different types of date formats either in sql or in PHP. MySQL offers the DATE_FORMAT function.
PHP can take almost any string describing a date and turn it into a universal time value using [man]strototime[/man] and then you can feed that to the [man]date[/man] function in order to format it however you like. E.g.:
// any one of these will probably work
$str = 'today';
$str = 'next wednesday';
$str ='2009-04-16 00:00:00'; // midnite last night
$str = 'January 1st, 1987';
$str = 'now';
$stamp = strototime($str);
echo date('Y-m-d H:i:s', $stamp);