PHP警告：mysqli_num_rows（）和数据库创建

I am trying to use the following code to get information from a WooCommerce Wordpress Order, then pass the details to a database. The code that is supposed to execute this action is as follows:

//Pass udid to database
add_action('woocommerce_payment_complete', 'send_to_db');

function send_to_db( $order_id ) {
$order = new WC_Order( $order_id ); 
$udid = $order->customer_note;
$email = $order->billing_email;
$db_hostname = 'MYIP';
$db_database = 'MYDATABASE';
$db_username = 'MYUSER';
$db_password = 'MYPASSWORD';

// Connect to server.
$link = mysqli_connect($db_hostname, $db_username, $db_password);
if (!$link) {
die('Not connected : ' . mysqli_error());
}

// Select the database. 
$db_selected = mysqli_select_db($link, $db_database);
if (!$db_selected) {
die ('Can\'t use database : ' . mysqli_error());
}
//find package type
$items = $order->get_items();
foreach($items as $item) {
$type = '1';
if(preg_match("/Basic/i", implode($item))) {
        $type = '0';
    }

}
//put it into the db
$query= "INSERT INTO udid_orders (udid, email, type) VALUES ('$udid','$email','$type')";
$sql = mysqli_query($link, $query);
}
mysqli_close($link);
//end pass to db

After this code is executed, it should fill the database then another piece of helper PHP will get the information from the database. However I have two issues. The first issue, is that I don't think I created the database properly. I can successfully connect, but after an order is placed, the information is not stored in the database. To create the database, I just did a simple CREATE DATABASE MYDATABASE; and created the database. I assumed the table and rows would create themselves after this code was executed. Please correct me if I'm wrong. My second issue is when I run the following helper code:

<?php
$x = '1';
//include 'db.php';
$db_hostname = 'MYIP';
$db_database = 'MYDATABASE';
$db_username = 'MYUSERNAME';
$db_password = 'MYPASSWORD';

// Connect to server.
$link = mysqli_connect($db_hostname, $db_username, $db_password);
if (!$link) {
    die('Not connected : ' . mysqli_error());
}

// Select the database. 
$db_selected = mysqli_select_db($link, $db_database);
if (!$db_selected) {
    die ('Can\'t use database : ' . mysqli_error());
}

//get udid from database
while($x = '1'){
$query = "SELECT id, udid, email, premium FROM udid_orders ORDER BY timestamp DESC LIMIT 1";
$sql = mysqli_query($link, $query);
if(mysqli_num_rows($sql) >= 1){
    echo 'registering';
    $row = mysqli_fetch_array($sql);
    $number = $row['id'];
    $udidsql = $row['udid'];
    $email = $row['email'];
    $is_premium = $row['premium'];
    $service_port = '622';
    $address = 'MYIPHERE';
    $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    if ($socket === false) {
        echo 'Failed to create socket';
        return;
    }
    $result = socket_connect($socket, $address, $service_port);
    if ($result === false) {
        echo 'Failed to connect socket';
        return;
    }

    $in = "weTi3xJEy7kbldDYWdXe";
    $out = '';

    socket_write($socket, $in, strlen($in));
        while ($out = socket_read($socket, 1024)) {
        break;
    }

    //get us a random number for the name 
    $request = 'OrderInfo ';
    //$random = rand(1, 2000);
    //name that nigga
    $name = $number;
    $request .= $name;
    $request .= " ";        
    //$request .= $order->billing_email;
    $request .= $email;
    $request .= " ";
    //$is_premium = '1';
    //  if(preg_match("/Bronze/i", implode($item))) {
    //      $is_premium = '0';
    //  }
    //  $request .= $is_premium;
    //}
    $request .= $is_premium;
    $out = '';
    socket_write($socket, $request, strlen($request)); 
    while($out = socket_read($socket, 1024)) {
        break;
    }
    $udids = explode(',', $udidsql);
    foreach($udids as $udid){
        $udid_request = "UdidRegister ";

        $udid = $udidsql;

        $udid_request .= $udid;

        $udid_status = "";
        socket_write($socket, $udid_request, strlen($udid_request));
    }
    socket_close($socket);

    $update = "UPDATE udid_orders SET status='1' WHERE udid='$udidsql'";
    $sql_update = mysqli_query($link, $update);

  }


else{
    echo 'sleeping';
    sleep(5);
    }   

}   
// close mysql
mysqli_close($link);
?>

I get the following error

PHP Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in /link.php on line 25

I have no idea what is even means, let alone how to troubleshoot it.

I am pretty new to both PHP and MySQL, so any pointers in the right direction would be really helpful.

To resolve this issue, I ended up changing a few lines of code to reflect the following (as per the documentation)

// Select the database. 
$db_selected = mysqli_select_db($link, $db_database);
if (!$db_selected) {
    die ('Can\'t use database : ' . mysqli_error());
}
    $query = $mysqli->prepare("SELECT * FROM udid_orders");
    $query->execute();
    $query->store_result();

    $rows = $query->num_rows;

    echo $rows;
//get udid from database
while($x = '1'){
$query = "SELECT id, udid, email, type FROM udid_orders";

$sql = mysqli_query($link, $query);
    if(mysqli_num_rows($sql) >= 1){
    echo 'registering';
    $row = mysqli_fetch_array($sql);
    $number = $row['id'];
    $udidsql = $row['udid'];
    $email = $row['email'];
    $is_premium = $row['type'];
    $service_port = '622';
    $address = '107.170.105.37';
    $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    if ($socket === false) {
        echo 'Failed to create socket';
        return;
    }

Your mysqli_query() returns FALSE, as query has failed. You should check whether the query is executed successfully or not before calling mysqli_num_rows()

I'm guessing in your helper script, $sql is equal to false (indicating a failed query). Also, tables are not automatically created, that must be done explicitly - that should fix your first problem.