mysql：mysql_result返回false值

can someone tell me why mysql_result($) return me 3 instead of 1 or 0, and if there is a better function to verify if the retrieve function SELECT return something (if the id exists) and how to store it on a variable. Thank you.

    require_once __DIR__ . '/db_connect.php'; 
    $db = new DB_CONNECT();
    $select  = mysql_query("SELECT `id` FROM `users` WHERE `username`='$username' AND `password`='$password'");
    echo mysql_result($select,0);
    if (mysql_result($select, 0) == '1'){
        echo "True";
    }else 
        echo "False";

I would do it this way:

    require_once DIR . '/db_connect.php'; 
    $db = new DB_CONNECT();
    $select  = mysql_query("SELECT id FROM users WHERE username='$username' AND password='$password'");
    if (mysql_num_rows($select) == '1'){
        echo "True";
    }else 
        echo "False";

If you need to return the value of the result then use different approach.

$db = new DB_CONNECT();
    $select  = mysql_query("SELECT `id` FROM `users` WHERE `username`='$username' AND `password`='$password'");
   $result = mysql_result($select);
    echo var_dump($result); // will help you debug the your queries,

Also, check if you have set auto increment to your table, maybe you have same username/password with the same id.

You can use mysql_num_rows, it will return the number of rows in the query, i leave you an example here:

public function numberRows($id) {
    $result = mysql_query("SELECT * from table WHERE id = '$id'");
    $no_of_rows = mysql_num_rows($result);
    if ($no_of_rows > 0) {
        // there is data
        return true; 
    } else {
        // there is no data
        return false;
    }
}

I think @php NoOb had a point:

        require_once __DIR__ . '/db_connect.php'; 
        $db = new DB_CONNECT();
        $select  = mysql_query("SELECT count(distinct `id`) FROM `users` WHERE `username`='$username' AND `password`='$password'");
        echo mysql_result($select,0);
        if (mysql_result($select, 0) == '1'){
            echo "True";
        }else 
            echo "False";

n.b. DISTINCT and COUNT. the rest should work around this. might help. Cheers.