Unable to solve PHP error message - php

Question

Can anyone please help me with the following error. I am making a register and login function for my website. I have it connected to my local database and in there I have created a user. When I test that I can login and that username and password is recognised, it works as expected. But I get this error
Warning: mysql_result(): Unable to jump to row 0 on MySQL result index 17 in C:\xampp\htdocs\LoginAndRegistration\core\functions\users.php on line 34
And this is what I have on line 34
return (mysql_result(mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'"), 0) == 1) ? true : false;
Which is part of the following function
function login($username, $password) {
$user_id = user_id_from_username($username);
$username = sanitize($username);
$password = md5($password);
return (mysql_result(mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'"), 0) == 1) ? true : false;
}
Ive been staring at it for ages now but cant seem to figure out the problem. Can anyone tell me what I am doing wrong?
Thanks

Answer 1

That line of code looks like that you want to check does username and password exist. You need to change your code to this:
return (mysql_result(mysql_query("SELECT COUNT(id) FROM users WHERE username = '$username' AND password = '$password'"), 0) == 1) ? true : false;
Also change (id) to your id name of column.

Answer 2

This error means the query failed. Always check if the query succeeded:
$q = mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'");
if ($q) {
if ($rows = mysql_num_rows($q)) {
// Continue operation, or set a flag
} else {
// No matching rows, throw an Exception or set a flag
}
} else {
// Something is wrong
die(mysql_error());
}

Answer 3

Your error probably comes from the fact that the query did not return any result at all because there was none with matching username and password.
I would really not stuff that much functions into each other. It looks overcomplicates, it does not leave any room to add error handling (like handling the case that is supposed to happen in your case), and it messes up PHP'S error reporting, because any error happening will be on the same code line.
Spread stuff out into multiple lines. It makes things clearer for you any anybody that reads your code, in enhances debugging activities, and is generally a good idea because of the lower line length.

Answer 4

You are getting a warning (not an error) because mysql_query at some times, it won't return any rows, so trying to get the first row with mysql_result when there are not rows, will raise the warning.
You can try:
function login($username, $password) {
$user_id = user_id_from_username($username);
$username = sanitize($username);
$password = md5($password);
$query = mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'");
if (mysql_num_rows($query) > 0)
return true;
else
return false;
}

Answer 5

With the depreciation argument aside, use mysql_num_rows instead of mysql_result.
function login($username, $password) {
$user_id = user_id_from_username($username);
$username = sanitize($username);
$password = md5($password);
return (mysql_num_rows(mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'")) == 1) ? true : false;
}

Answer 6

try this
function login($username, $password) {
$user_id = user_id_from_username($username);
$username = sanitize($username);
$password = md5($password);
$query = mysql_query("SELECT * FROM users WHERE username = '$username' AND password = '$password'") ;
if (mysql_num_rows($query) > 0 ) {
$data = true ;
}else {
$data = false ;
}
return $data ;
}