MySQL Injection Problem

Question

I've been coding my website in PHP lately and I was pretty proud of myself for my good practices of sanitizing my input before I used it in a query. It was all going great until my friend said I need to sanitize my input. When I tried to explain to him that it was sanitized, he showed me that he had found everything in 'users' table in my database. I didn't know how, so I thought I would post what I was doing wrong that made my sanitizing not work. Here is the PHP code he was exploiting:

start_mysql(); // Starts the databases stuff, etc.

$id = mysql_real_escape_string($_GET['id']);
$game = mysql_query("SELECT * FROM `games` WHERE `id` = $id LIMIT 0, 1");

All he was doing was changing the id parameter, making him able to use SQL injection on my database. I thought mysql_real_escape_string escaped all characters like that, but apparently I was wrong. I did some tests with a normal string to see what would happen, and this is what it said

URL: /game.php?id=' OR '' = '

echo($_GET['id']); // This echo'd: \' OR \'\' = \'
echo(mysql_real_escape_string($_GET['id'])); // This echo'd: \\\' OR \\\'\\\' = \\\'

So, my simple question is, what am I doing wrong?

Answer 1

You need to put the escaped string in single quotes:

WHERE `id` = '$id' 

Answer 2

Since id was an integer parameter and you did not surround it in single-quotes in your SQL, the value of $id is sent directly into your query. If you were expecting an integer id, then you should verify that the value of $_GET['id'] is a valid integer.

$id = intval($_GET['id']);