Using Checkboxes to Update a MySql Database

Ok, I know I'll probably get bashed for even asking this... its been about 5-6 years since I've touched PHP and MySql, so I think I may be overthinking all of this.

I have an HTML form, that is a series of checkboxes, and by clicking one, I would like it to set it's relative entry in the database to 0 or 1. When the update is complete, it returns to the form so I can change the settings again if needed.

The amount of entries (checkboxes) will be a static amount will be static, so I don't think a foreach loop will be necessary, I'm more or less trying to jog my memory on how to work with PHP, and I'm not having much luck reading a whole mess of answers scattered about SO that kinda have to deal with what I'm trying to do.

Any help will be greatly appreciated.

FORM:

<?php

 require "config.php";

 $db = mysql_connect($db_host, $db_user, $db_pass) or die(mysql_error());
 mysql_select_db($db_name) or die(mysql_error());

 $query = "SELECT * FROM roster";
 $result = mysql_query($query);

?>
<form action="update.php"  method="POST">
<?php

        while( $row = mysql_fetch_array($result) ){
            $active = $row['active'];
            $name = $row['name'];
            $class = $row['class'];
            $value = '0';

            if ($active == '1'){
                $value = '0';
            } else {
                $value = '1';
            }

            echo "<label class='switch'><input type='checkbox' name='".$class."' value='". $value."'";

            if($active == '1'){
                echo "checked='checked'";
            }

            echo "/><div class='slider'></div><span>" . $name . "</span></label>";
        }

 mysql_close();
 ?>
<input type="submit" class="submit" value="Update Active Roster">
</form> 

Update.php (so far) - this is where I need help, I think

<?php
require "config.php";

$db = mysql_connect($db_host, $db_user, $db_pass) or die(mysql_error());
mysql_select_db($db_name) or die(mysql_error());

$checkbox = $_POST['activate'];
for($i = 1; $i < sizeof($checkbox)+1; $i++){
    $query = "UPDATE roster SET active='".$checkbox[$i]."' WHERE id='".$i."'";
    echo "active='".$checkbox[$i]."' WHERE id='".$i."'";
    mysql_query($query) or die(mysql_error());
}

?>

MySQL Database

id   class      name         active
0    thisdude   This Dude    0
1    thatguy    That Guy     0
2    somechick  Some Chick   0