为什么我从这段代码中得到“Query is empty”错误？

Question

I'm trying to make a login/register system and when you press login it should say exists...

<?php
include 'core/init.php';


function user_exists($username){
$username = sanitize($uusername);
$query = mysql_query("SELECT COUNT (`user_id`) FROM `users` WHERE `username` = '$username'");

$result = mysql_query($query) or die(mysql_error());  // Check if query was successful
$row = mysql_fetch_array($result); // fetch the first row
return ($row[0] > 1);  // If there is one or more users with this name, return true.




}

Here is the code that should make the page say "Exists":

<?php
include 'core/init.php';

if(user_exists('Zuzima') === true) {
echo 'exists';
}
die();

if (empty($_POST) === false) {
$username = $_POST['username'];
$password = $_POST['password'];

if(empty($username) === true || empty($password) === true){
    $errors[] = 'You need to a username and password.';
} else if (user_exists($username) === false) {
    $errors[] = 'We can\'t find that username. Have you registered?';
}
}
?>

Please help me I've been working on this for 6 months at the least.

Answer 1

If there is one or more users with this name, return true.

So shouldn't return ($row[0] > 1); just be return ($row[0] >= 1);

Answer 2

You must alias any aggregates to use in an array.

SELECT COUNT (`user_id`)  AS userIdCount ...

It would just be easier to return a single column and use the row count to determine if there is a record for your user.

Further, mysql_ functions have been deprecated. You need to use PDO or mysqli_ with prepared statements.

Answer 3

The $query is getting assigned a resource handle from mysql_query , then you are passing that resource handle in as a string to mysql_query

$query = mysql_query("SELECT COUNT (`user_id`) FROM `users` WHERE `username` = '$username'");

$result = mysql_query($query) or die(mysql_error());

should be

$result = mysql_query("SELECT COUNT(`user_id`) FROM `users` WHERE `username` = '$username'") or die(mysql_error())