PHP cannot show tables from MySqli Query

Question

I am trying to figure out why I can connect to a database, but cannot access the data in it.

Here's my configuration:

//config.php
<?php
define("HOST", "MYSERVERNAMEISHERE");
define("DATABASE", "users");
?>

My user logs in, and their information is passed to be checked:

//login.php
<?php
if ($_POST) {
    if ($_POST["user"] && $_POST["password"]) {
        include_once "config.php";
        define("USER", $_POST["user"]);
        define("PASSWORD", $_POST["password"]);
        $link = new mysqli(HOST, USER, PASSWORD, DATABASE);
        if ($link) {
            $link->close();
            if ($_SESSION) {
                session_destroy();
            }
            session_start();
            $_SESSION["user"] = $_POST["user"];
            $_SESSION["password"] = $_POST["password"];
        }
    }
}
if ($_SESSION) {
    header('Location: profile.php');
}
else {
    header('Location: login.html');
}
?>

When they pass, they get to see their profile page.

//profile.php
<?php
session_start();
if (!$_SESSION["user"] || !$_SESSION["password"]) {
    session_destroy();
    header("Location: login.html");
}
else {
    include_once "config.php";
}
$link = new mysqli(HOST, USER, PASSWORD, DATABASE) or die("Unable to connect to database");
$result = $link->query("SHOW TABLES") or die("Unable to show tables");
...
ADDITIONAL PHP AND HTML CODE AFTER THIS POINT

The problem is that the process dies when I try to query the mysqli link. (I get Unable to show tables) Right now, the SHOW TABLES is just filler for debugging; I will actually have useful mysqli queries when I figure out the issue.

Please help me determine where my bug is. If you find a typo or a reference link for me, sorry for wasting your time. I've been researching and debugging for hours now.

Thanks very much in advance.

PS: If you have some good advice for changes I should make, I appreciate those too. It's my first time making a user login.

Answer 1

Your query in profile.php is failing because USER and PASSWORD are not defined. When the person logs in, they are defined in login.php. When redirected to profile.php, USER AND PASSWORD do not have values since they are not in config.php.

In profile.php, change

$link = new mysqli(HOST, USER, PASSWORD, DATABASE) or die("Unable to connect to database");

to

$link = new mysqli(HOST, $_SESSION["user"], $_SESSION["password"], DATABASE) or die("Unable to connect to database");