gettin records from today, yesterday, etc.

Hi there, I am wondering how to get recors out of a mysql db from yesterday, last week and last month. I did write a small php hack but this does not work properly. I did this: ################################################### switch ($ts){ case 1: // today $timestamp = substr($timestamp,0,8).'000000'; break; case 2: // yesterday $timestamp = (substr($timestamp,0,8)-1).'000000'; break; case 3: // last week $timestamp = (substr($timestamp,0,8)-7).'000000'; break; }; $start_date = $timestamp; $display_option = "AND p.timestamp > '$start_date'"; ################################################### But it leads to problems if I search for last week since I do a siple subtraction of integer values and not of real days. Maybe some of you guys has a better appoach? Thanx, Andy