PHP MySQL. Add table contents does not work - php

Question

If I want to add content to the table using "INSERT INTO", I don't get an error message and the table is not filled. I'm new with PHP. explanations would be nice. The database runs on XAMPP.
I don't know what to try. I've already used another table, but it doesn't work. The user should have full access to the table. The names also match.
<?php
$username = $_POST["username"];
$passwort = $_POST["passwort"];
$mail = $_POST["mail"];
$passwort2 = $_POST["passwort2"];
$pass = sha1($passwort);
$db = mysqli_connect("localhost", "phptest1", "o84XM5wxo65QBjkF", "phptest1");
if($passwort == $passwort2) {
echo "Password is correct.";
$db = "INSERT INTO user (Username, Mail, Password) VALUES ('$username', '$mail', '$pass')";
} else if(!($passwort == $passwot2)) {
echo "Password is not correct";
} ?>

Answer 1

The variable $db actually contains information about the connection. You cannot insert a query into your database the way you are trying to
You can use $db (in your case) in order to check whether the connection has been correctly established or not and then if everything works correctly you can user mysqli_query() to inject the query into your database.
You can do it like so:
<?php
if(isset($_POST['submit'])){ //You have to check if your submit button is pressed
$username = $_POST["username"];
$passwort = $_POST["passwort"];
$mail = $_POST["mail"];
$passwort2 = $_POST["passwort2"];
$pass = sha1($passwort);
$db = mysqli_connect("localhost", "phptest1", "o84XM5wxo65QBjkF", "phptest1");
if(!$db){
die('Connection could not be established! Check provided information');
}
if($passwort == $passwort2) {
echo "Password is correct.Inserting query now";
$query = "INSERT INTO user (Username, Mail, Password) VALUES ('$username', '$mail', '$pass')";
$result = mysqli_query($db, $query); //keep $result for debugging purposes.
} else {
die("Password is not correct");
} //no need for else if as there are only 2 conditions.
if(!$result){ //check if query was successful.
die('Query Error');
}
echo "Query Updated successfully";
}
?>
This code is really simplistic and for testing purposes only.
I just wanted to show you the way you can send queries to your database. You better use other encryption techniques i.e. crypt() and of course functions like mysqli_real_escape_string() when retrieving data from users, in order to avoid potential injection attacks.
Check this post for more info about preventing injections.
Hope that helps.