我如何回显表中的行数并在零行时显示警报

Question

我无法回显行数，如果行数为零，则不会显示警报。

  

警告：mysqli_query（）至少需要2个参数，在 45 <45>行的 C：\ xampp \ htdocs \ cart7 \ cart_view.php 中给出1个参数。 / strong>
  警告：mysqli_fetch_assoc（）期望参数1为mysqli_result，在 C：\ xampp \ htdocs \ cart7 \ cart_view.php 中给定null

<?php
    include 'includes/conn.php';
    session_start();

    $result=mysqli_query("SELECT count(*) as total from cart");
    $data=mysqli_fetch_assoc($result);
    echo $data['total'];
    if(!$data) {
        echo "<script>
        alert('Empty Cart');
        {
            window.location.href='index.php';
        }
    </script>";
}

if(isset($_SESSION['admin'])){
    header('location: admin/home.php');
}
if(isset($_SESSION['user'])){
    $conn = $pdo->open();
    try{
        $stmt = $conn->prepare("SELECT * FROM users WHERE id=:id");
        $stmt->execute(['id'=>$_SESSION['user']]);
        $user = $stmt->fetch();
    }
    catch(PDOException $e){
        echo "There is some problem in connection: " . $e->getMessage();
    }
    $pdo->close();
}
?>

我已经尝试过了，但是仍然无法正常工作

$result=mysqli_query("SELECT count(*) as total from cart");
    $data=mysqli_fetch_assoc($result);
    echo $data['total'];
    if(!$data){
}