如果{}，则使用isset的有效方法

I was wondering: I use this code:

if($_GET['rvr_filter_select'] == $qRows) {
    $sSelected = 'selected';    
}

But in this case when php doesnt get rvr_filter_select it gives a error of a undifined index rvr_filter select

Now I was wondering of this is a valid way to solve this problem. It doesnt output the error anymore but I dont know if it will work the same as the code above:

if(isset($_GET['rvr_filter_select']) == $qRows) {
    $sSelected = 'selected';    
}

You should use

if(isset($_GET['rvr_filter_select']) && $_GET['rvr_filter_select'] == $qRows) 

The isset function returns a boolean: true or false.

Thats not going to work, because you will first validate if the value is set, this will be true of false and then compare it to $qrows, you should do both for best results..

if(isset($_GET['rvr_filter_select']) && $_GET['rvr_filter_select'] == $qRows) {
    $sSelected = 'selected';    
}

The isset function returns a boolean: true or false.

if(isset($$_GET) && isset($_GET['rvr_filter_select']) && $_GET['rvr_filter_select'] == $qRows){
    $sSelected = 'selected';
} 

if(isset($_GET['rvr_filter_select']) && trim($_GET['rvr_filter_select']) == $qRows) {
    $sSelected = 'selected';    
}
else
{
}