MySQL Datediff()

Zwraca ilość dni pomiędzy dwoma datami lub znacznikami czasu

DATEDIFF( expr1, expr2 );

SELECT DATEDIFF( '2008-05-17 11:31:31','2008-04-28' ) ;

+----------------------------------------------+
| DATEDIFF('2008-05-17 11:31:31','2008-04-28') |
+----------------------------------------------+
|                                           19 | 
+----------------------------------------------+