I'm trying to update a row so that the value of a cell (shown)is equal to the date difference between the timestamp in another cell (time)and the current time.

I'm using MySQL, and this is what I have, but it doesn't seem to work.

Any suggestions? Thanks.

mysql_query("UPDATE mytable SET shown=DATEDIFF(time,'".date("Y-m-d H:i:s")."') WHERE ip='$ip'");