the long way is

<?php
$sql_query = mysql_query("SELECT `number` FROM `numbers` WHERE `pageid` = '$pageid'", $link);
while($rs = mysql_fetch_array($sql_query)) {
$num = $rs[0] + 1;
}
$sql_query = "UPDATE `numbers` SET `number` = '$num' WHERE `pageid` = '$pageid'";
if(mysql_query($sql_query)) {
echo "Record updated successfully";
}
?>

the short way

UPDATE table SET foo = foo +1 WHERE bar = x