Converting To MYSQLI - php

Question

I'm working to convert to MYSQLi. something i'm not entirely confident in just yet. I'm getting an error trying to breakdown this portion of my script.
<?php
// Parse the form data and add inventory item to the system
if (isset($_POST['username'])) {
$username = $_POST['username'];
$password = $_POST['password'];
$level = ($_POST['level']);
// See if that product name is an identical match to another product in the system
include "includes/db_conx.php";
$sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
$user_query = mysqli_query($db_conx, $sql);
$productMatch = mysqli_num_rows($sql); // count the output amount
if ($productMatch > 0) {
header("location: message.php?msg=usererror");
exit();
}
// Add this product into the database now
$username = preg_replace('#[^a-z0-9]#i', '', $_POST['username']);
$ip = preg_replace('#[^0-9.]#', '', getenv('REMOTE_ADDR'));
$email = mysqli_real_escape_string($_POST['email']);
$p_hash = md5($password);
$sql = mysqli_query("INSERT INTO users (username, password, ip, email, level, date_added)
VALUES('$username','$p_hash','$ip','$email','$level',now())") or die (mysql_error());
header("location: order_complete.php");
exit();
}
?>
I believe I've got most of it down, but the second half of this is giving me fits. I'm trying to establish past
// Add this product into the database now
a mysqli conversion. I just can't seem to keep myself from mangling the script and throwing all kinds of errors. I believe I'm about half way there, but introducing select is throwing me off. Can someone help me to figure out this.

Answer 1

You are passing the $sql as a param to mysqli_num_rows() and it should be the result of a mysqli_query().
So change to this.
$sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
$user_query = mysqli_query($db_conx, $sql);
$productMatch = mysqli_num_rows($user_query); // count the output amount
A better name for that variable might be $user_result or something with the word result in.

Answer 2

Check the below mentioned code.
if (isset($_POST['username'])) {
$username = $_POST['username'];
$password = $_POST['password'];
$level = ($_POST['level']);
// See if that product name is an identical match to another product in the system
include "includes/db_conx.php"; // I guess it has $db_conx = mysqli_connect("localhost", "my_user", "my_password", "world");
$sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
$user_query = mysqli_query($db_conx, $sql);
$productMatch = mysqli_num_rows($user_query); // count the output amount
if ($productMatch > 0) {
header("location: message.php?msg=usererror");
exit();
}
// Add this product into the database now
$username = preg_replace('#[^a-z0-9]#i', '', $_POST['username']);
$ip = preg_replace('#[^0-9.]#', '', getenv('REMOTE_ADDR'));
$email = mysqli_real_escape_string($db_conx, $_POST['email']);
$p_hash = md5($password);
$sql = mysqli_query($db_conx, "INSERT INTO users (username, password, ip, email, level, date_added) VALUES('$username','$p_hash','$ip','$email','$level',now())") or die (mysqli_error($db_conx));
header("location: order_complete.php");
exit();
}