Use an IF STATEMENT with INSERT IGNORE

I have a voting system, which users can use to vote on posts. Thing is, they can't vote twice on the same post. Which is good. I did that like this:

$query  = "INSERT IGNORE INTO vote_id (vote, postid, userid) 
        VALUES ('1', '{$postid}', '{$userid}')";    
$result = mysqli_query($db, $query);
header('Location: index.php');

(The $db is my variable that connects to the database).

They can still click on the vote, even if it doesn't insert into the table.

My problem is:

When it is "IGNORE" they shouldn't be able to click.



My question is:

How do I separate the INSERT and IGNORE, so I can use the IGNORE in an IF statement? Or in any other way, that can change the layout of the page.



Thanks in advance! Really struggling with this one.