PHP and MySQL user accounts [duplicate] - php

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Reference - What does this error mean in PHP?
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I'm very new to both PHP and MySQL.
I have only begun to learn them to run a game server.
The problem I have run into is descriped in apache error log as:
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP Notice: Undefined variable: db in C:\Program Files\VertrigoServ\www\sw_game_login.php on line 24
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP Stack trace:
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP 1. {main}() C:\Program Files\VertrigoServ\www\sw_game_login.php:0
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP Fatal error: Call to a member function fetch_row() on null in C:\Program Files\VertrigoServ\www\sw_game_login.php on line 24
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP Stack trace:
[Mon Sep 04 01:00:16.928467 2017] [:error] [pid 3656:tid 784] [client 127.0.0.1:49401] PHP 1. {main}() C:\Program Files\VertrigoServ\www\sw_game_login.php:0
line 24 of sw_game_login.php looks like the following:
if(list($id)=$db->fetch_row($db->query("SELECT ID FROM accounts WHERE ACCOUNT_NAME='$account' AND ACCOUNT_PASSWORD='$pass'"))){
The error I receive from my game client says that incorrect account or password, I know this is not the case I have tried several and checked several times. Thus leading me to believe that maybe the request is not being sent through properly.
Thanks in advance to any help!

Answer 1

According to your error log, your db variable is undefined. Add this to the top of your sw_game_login.php script.
if (!isset($db))
$db = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);