How can I limit the max value of number in mysql?

Question

I've been creating a voting system and I've noticed that the users are still able to vote again after logout.
What I'm trying to do is to add a variable to vote, now button, and set its maximum value to 1 to prevent the user from voting again.

Is there any suggestion or way to achieve this so users will not be able to vote again like?

$errors = array(); 
$db = mysqli_connect("localhost", "root", "", "registration");
if (isset($_POST['votenow'])) {
    $user_check_query = "SELECT * FROM users WHERE votenow = '$votenow'";
    $votenow = "update users set votenow = votenow + 1";
    $run_vote = mysqli_query($db, $votenow);
    if ($votenow > 1 ) {
        echo "No more votes can be added.";
    } 
    if ($run_vote) { 
        header( "Location: renewsys3.php" ); 
    } 
}

I've been also trying this but the users can still vote again. The votes were working that limits to 1 vote but the users are still being redirect to next page instead of returning. renewsys2re is the current page and renewsys3 is the next page.

<?php
$errors = array(); 
$db = mysqli_connect("localhost","root","","registration");

    if(isset($_POST['votenow']))
    { 

    $votenow = "update users set votenow = votenow + 1 where votenow < 1 
    LIMIT 1";

    $run_vote = mysqli_query($db,$votenow);

    if ($votenow == 2 ){
    echo '<script type="text/javascript">alert("Once!");</script>';
    header ("Refresh:0; url=renewsys2re.php");
    }

    else{
    echo '<script type="text/javascript">alert("Welcome!");</script>';
    header ("Refresh:0; url=renewsys3.php");
}
}
?>

Answer 1

You have to maintain $_SESSION variable after user login and logout.You have to store and compare user_id and modified your query of checking votes to $user_check_query = "SELECT * FROM users WHERE user_id=:user_id and votenow=:votenow";

Use bindparams to add security from sql injection.