无法解决错误消息php：尝试设置验证密钥

Question

嗨大家好，我仍然无法解决此错误消息：

警告：mysqli_num_rows（）要求参数1为mysqli_result，布尔值在第11行的C：\ wamp64 \ www \ listing \ verify.php中给出

我尝试了不同的建议，但我仍然无法弄清楚如何解决它。

这是代码：

<?php 
require_once('connect.php');

$key = isset($_GET['key']);
$id = isset($_GET['id']);

$sql = "SELECT * FROM usermanagement WHERE id=$id AND verify_key='$key' AND active=0";
$res = mysqli_query($connection, $sql);

/* determine number of rows res set */
$count = mysqli_num_rows($res);

if($count == 1){
    $usql = "UPDATE usermanagement SET active=1 WHERE id=$id";
    $ures = mysqli_query($connection, $usql);
    if($ures){
        $successmsg = "Account Activated Successfully";
    }
    else{
        $failmsg = "Account Activation failed, contact support";
    }
}
else{
    $failmsg = "key not found in db";
}

?>