mysqli_query在主机上返回NULL但在本地主机上运行

Question

I have small php web service and I tested it locally and it works. When I uploaded it to bluehost server I get NULL as a result from calling mysqli_query

$con = connect();
    $userName = mysqli_real_escape_string($con, $userName);
    $email = mysqli_real_escape_string($con, $email);

    $query1 = "select * from `users` where `user_name` = '$userName'";

    $res1 = mysqli_query($con, $query1);
//var_dump($res1)  prints NULL

    if ($res1) {
        $count = mysqli_num_rows($res1);

        if ($count == 0) {
            $query2 = "select * from `users` where `email` = '$email'";
            $res2 = mysqli_query($con, $query2);
            if ($res2) {
                $count2 = mysqli_num_rows($res2);
                if ($count2 == 0) {
                    return 0; //not found before
                } else {
                    return 2; //Email already exists
                }
            }
        } else {
            return 1; //user name already exists
        }
    } else {
        return -1;   //Database Error; // always resturned
    }

Edit 1: //Code to connect to database function connect() {

    $con = mysqli_connect("localhost", "user", "pass", "db");
    if (mysqli_connect_errno()) {
        return 0;
    } else {
        return $con;
    }
}

EDIT 2: If I added mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); in the first line at connect() method, I got nothing at all, even the -1 return is not there.

Answer 1

It was a problem in the database structure and I don't know why mySqli did not show this when I print the error messages. I imported the sql dump file and it worked. Sorry and Thanks for your time.