Through this example i think you can better understand
if ( !filter_has_var(INPUT_GET, 'email') ) {
echo "Email Not Found";
}else{
echo "Email Found";
}
Output
localhost/nanhe/test.php?email=1 //Email Found
localhost/nanhe/test.php?email //Email Found
http://localhost/nanhe/test.php //Email Not Found
Consider on second example
http://localhost/nanhe/test.php
$_GET['email']="info@nanhe.in";
if ( !filter_has_var(INPUT_GET, 'email') ) {
echo "Email Not Found";
}else{
echo "Email Found";
}
But output will be Email Not Found