Executing query through HTML form - php

Question

views/registration.php
<form action="classes/registration.php" method="post">
Username: <input type="text" name="username"><br>
Password: <input type="text" name="password"><br>
<input type="submit">
</form>
classes/registration.php
if(isset($_POST['submit']))
{
// Define form variables
$username = $_POST['username'];
$password= $_POST['password'];
// Insert form data into database
$query = "INSERT INTO users (username, password)
VALUES ('$username', '$password')";
if(mysqli_query($conn, $query))
{
echo "Registration successfull.";
}
}
The problem is, when I click submit, I get a blank page. The query isn't being executed.
I thought the problem might be because my values aren't setup correctly, so I did the following:
VALUES ('$_POST['password']', '$_POST['password']')";
but that gives me an error, presumably because I am using ' inside of '
So now I am back to square one, unsure of why my query isn't being executed

Answer 1

You are getting a blank page because you don't echo something if $_POST submit isn't set.
if(isset($_POST['submit']))
is never true as your $_POST['submit'] is never set. You need to give your submit a name, this (the name) is what get's POSTed / what you can access within $_POST[' /*name of input*/ ']
Change your form to the following, then you should see your
echo "Registration successfull.";
HTML:
<form action="classes/registration.php" method="post">
Username: <input type="text" name="username"><br>
Password: <input type="text" name="password"><br>
<input type="submit" name="submit"> <!-- <<<<<<<<<<< here -->
As a sidenote, you should absolutely consider using a prepared statement. Running a registration form with your insert query is like an invitation for people keen on ruining your server. You might want to try the query like this:
$query = $conn->prepare("INSERT INTO users (username, password) VALUES (?,?)");
$query->bind_param('ss',$username,$password);
$query->execute;
This way, you will be secured against mysql injection.

Answer 2

Your file naming and paths seem to be mismatching(as per the file names you provided).
No matter if you keep:
views/registration.php
views/classes/registration.php
But if you follow:
--/classes
/registration.php
--/views
/registration.php
[Note: '--/' is the path of your root directory]
Then the form action classes/registration.php won't go anywhere.
So change it:
<form action="../classes/registration.php" method="post">
I suggest to follow the naming convention:
filename- for pages with HTML forms, and
filename_action- for action pages
Also notice the possible error cases mentioned by user baao in the other answer.