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.

Please use PHP's built-in functions to handle password security. If you're using a PHP version less than 5.5 you can use the password_hash() compatibility pack. Make sure that you don't escape passwords or use any other cleansing mechanism on them before hashing. Doing so changes the password and causes unnecessary additional coding. — Jay Blanchard
– Jay Blanchard, Commented Apr 25, 2016 at 22:28
I do not see where you're querying the database. You appear to be allowing every user access to your database....which is not likely. — Jay Blanchard
– Jay Blanchard, Commented Apr 25, 2016 at 22:28
instead of using that measly unable to show tables message, use ->error property instead — Kevin
– Kevin, Commented Apr 25, 2016 at 22:38
@JayBlanchard I guess I was right about a comment I deleted in regards to USER and PASSWORD not being defined, hah. — Funk Forty Niner
– Funk Forty Niner, Commented Apr 25, 2016 at 22:48
possible duplicate of PHP: Notice: Undefined variable and Notice: Undefined index — Funk Forty Niner
– Funk Forty Niner, Commented Apr 25, 2016 at 22:48

fislerdata · Accepted Answer · 2016-04-25 22:42:08Z

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");

answered Apr 25, 2016 at 22:42

fislerdata

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1 Comment

GarrettML Over a year ago

I just found it myself. I marked as correct. Would upvote if I could. I also found that I was not properly vetting the login information. Thanks for the quick response.

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