Prepared statements using MySQL not inserting POST values to database table - php

Question

I'll be honest in saying I'm a rookie coder who knows the basics but is trying to learn more, this issue is also the reason I made an account as well as it's really stumped me. Lots of my code is temporary and I'm planning to streamline it later as well as adding features such as asterisks replacing the password input.
The desired outcome of my code is that the value of the variables below should be compared against those in my database table depending on the value of $type. The problem I'm encountering is that no entries are added to my database table. I'm unsure of where the problem lies within my code and I could do with a point in the right direction, this is my first application of prepared statements so I might be using them incorrectly
Main script:
<?php
include connect.db;
//These are normally user inputs from a form in another file.
$type = "students";
$username = "usernametest";
$password = "passwordtest";
$email = "emailtest";
//the connect global initilizes a connection between my database.
$query = $GLOBALS["conn"]->query("SELECT * FROM '$type' WHERE (username = '$username') OR (password = '$password') OR (email = '$email')");
if (mysqli_num_rows($query) == false) {
$stmt = $GLOBALS["conn"]->prepare("INSERT INTO ? (username, password, email) VALUES (?,?,?)");
$stmt->bind_param("ssss", $type, $username, $password, $email);
$stmt->execute();
$stmt->close();
echo "User Registered";
}
else {
echo "Username, password or email are already used";
}
?>
Connection Script:
<?php
//Identifies the databases details.
//Identifies the servername the database is created in
$servername = "localhost";
//Identifies the databases username
$username = "htmltes7";
//Identifies the database password
$password = "(mypassword)";
//Identified the afformentioned databasename
$dbname = "htmltes7_dbname";
/*Creates a new global variable which opens a connection between my database
using the variables above */
$GLOBALS["conn"] = new mysqli($servername, $username, $password, $dbname);
/*IF the connection cannot be made then the equilivent of exit() occours
in the form of die(). An error message is displayed containing information
on the error that occoured using mysqli_connect_error.*/
if (!$GLOBALS["conn"]) {
die("Connection failed: " . mysqli_connect_error());
}
?>
edit: Sorry about my poor formatting and incorrect tag usage first time round, like I said I'm new to both sql and stack overflow and kinda jumped the gun to ask my question. I've made changes based on the feedback and won't reproduce the same mistake in future.

Answer 1

Try to see the errors
error_reporting(E_ALL);
ini_set('display_errors', 1);
if (!$stmt) {
echo "\nPDO::errorInfo():\n";
print_r($dbh->errorInfo());
}