i have this code
<?php 
if(isset($_GET['qry'])) {
  echo $_GET['qry']; 
}
else if(isset($_GET['ct'])) {
  echo $_GET['ct']; 
}
else if(isset($_GET['sct'])) {
  echo $_GET['sct']; 
}
else if(isset($_GET['brand'])) {
  echo $_GET['brand']; 
} 
else {
 echo "";
}
?>
how do i properly protect the value i get from the page url from sql injection or other things since i use the value on the page or database.
I have searched and am seeing different method, please which do you think is the best way.
