查询mysqli_num_rows（）错误，期望参数1为mysqli_result

Question

有人可以告诉我如何解决此问题吗？

错误代码：

  

警告：mysqli_num_rows（）期望参数1为mysqli_result，布尔值       在第32行给出

我已经尝试了其他来源的帮助，但仍然无法解决该错误。谢谢。

<?php 

session_start(); 


 $connection = mysqli_connect("cust-mysql-123-20", "******", 
"********");
if (!$connection) {
    die("Database connection failed: " . mysqli_connect_error());
}


// Selecting a database 

$db_select = mysqli_select_db($connection, "tpdoadmin");
if (!$db_select) {
    die("Database selection failed: " . mysqli_connect_error());
}

$firstname = $_POST['firstname'];   
$surname = $_POST['surname'];
$date = $_POST['date'];
$address = $_POST['address'];
$user = $_POST['user'];
$password = $_POST['password'];
$email = $_POST['email'];
$phone = $_POST['phone'];

$s = "select * form usertable where user = '$user'"; 

$result = mysqli_query($connection, $s); 

$num = mysqli_num_rows($result);

if ($num == 1) {
echo" Your chosen usernmae is already taken."; 

}else{
$reg= "insert into usertable(user, firstname, surname, date, address, 
password, email, phone) values ('$user', '$firstname', '$surname', '$date', 
'$address', '$password', '$email', '$phone')";
mysqli_query($connection, $reg);
}