Mysql if PHP中的语法

Question

I need some help with PHP & Mysql. Can I use MySQL if-statement instead of this. thanks.

if ($last_id > 0) {
    $query = mysql_query("select * from chat where chat.to = '".$_SESSION['user_id']."' and id < '".$last_id."'");
}else{
    $query = mysql_query("select * from chat where chat.to = '".$_SESSION['user_id']."' ");
}

Answer 1

You can simplify this like

$last_id_query = '';
if ($last_id > 0) {
    $last_id_query .= " and id < '".$last_id."'";
}
$query = mysql_query("select * from chat where chat.to = '".$_SESSION['user_id']."' ".$last_id_query);