How to get Values and insert into mysql, and check if they posted before?

I want to find an easier route and securing this code or a possibly new securer way to do so.

if(isset($_GET['func'])&&isset($_GET['sid'])){    
  if($_GET['func'] == "subscore"){             
     $check_rates_res =    mysql_query("Select    * FROM user_shoutbox_comment_rates WHERE    Username='".$Call_User_Info->Username."'    AND comment_id='".$_GET['sid']."'");                 
     $rate_checker =    mysql_num_rows($check_rates_res);     
     if($rate_checker >= 1){    
        header("Location: index.php"); 
     }    
     if($rate_开发者_Go百科checker == 0){ 
        $sql_query =    "INSERT INTO    user_shoutbox_comment_rates    (Username, comment_id, comment_rate)    VALUES    ('".$Call_User_Info->Username."','{$_GET['sid']}','-1')    ";  
        mysql_query($sql_query);    
        header("Location: index.php"); 
     }
 }

}

@Gotactics when both time u r sending user to same page(index.php) then why don't you use below way

if(isset($_GET['func'])&& isset($_GET['sid']))
{    
  if($_GET['func'] === "subscore")
  {             
     $check_rates_res = mysql_query("SELECT * FROM user_shoutbox_comment_rates WHERE  Username='".$Call_User_Info->Username."'  AND comment_id='".$_GET['sid']."'");                 
     $rate_checker =   mysql_num_rows($check_rates_res);     
     if($rate_checker == 0){ 
        $sql_query  =  "INSERT INTO  user_shoutbox_comment_rates    (Username, comment_id, comment_rate)    VALUES    ('".$Call_User_Info->Username."','{$_GET['sid']}','-1')    ";  
        mysql_query($sql_query);
    }
    header("Location: index.php"); 
 }
}

i did not update any of your query... i just modify

u can see here INSERT ON DEPLICATE KEY UPDATE SYNTAX

edit

first u create unique key combination of 2 columns unique.

ALTER TABLE user_shoutbox_comment_rates ADD UNIQUE (Username,comment_id);

then u can use below query

$stmt ="INSERT INTO user_shoutbox_comment_rates
SET Username='".$Call_User_Info->Username."', comment_id=".$_GET['sid'].", comment_rate=-1
ON DUPLICATE KEY UPDATE comment_rate=-1";

despite the sql injection issue, you can combine both into this

insert ignore into ...