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$query = mysql_query("UPDATE `ip` SET `last_time`='$ct' WHERE last_time<='$t'") or die(mysql_error());
if(mysql_affected_rows($query) >0){
$add = true;
}else{
$add = false;
}

Warning: mysql_affected_rows(): supplied argument is not a valid MySQL-Link resource in C:\Program Files\...\file.php on line 133

if( mysql_affected_rows() > 0)
{
   ...
}