id | f_name | l_name | position | paygrade | users_id |..|

id | username | password | user_level | user_roles | email | employee_id

<?php
//If the POST var "register" exists (our submit button), then we can
//assume that the user has submitted the registration form.
if(isset($_POST['register'])){

    //Retrieve the field values from our registration form.

    //to be inserted in employee table
     $first_name = !empty($_POST['first_name']) ? trim($_POST['first_name']) : null;
     $last_name = !empty($_POST['last_name']) ? trim($_POST['last_name']) : null;
     $email = !empty($_POST['email']) ? trim($_POST['email']) : null;
    $phone = !empty($_POST['phone']) ? trim($_POST['phone']) : null;
     $company_name = !empty($_POST['company_name']) ? trim($_POST['company_name']) : null;
     $subdomain_name = !empty($_POST['subdomain_name']) ? trim($_POST['subdomain_name']) : null;

     //to be inserted in users table
    $username = !empty($_POST['username']) ? trim($_POST['username']) : null;
    $password = !empty($_POST['password']) ? trim($_POST['password']) : null;

    //TO ADD: Error checking (username characters, password length, etc).
    //Basically, you will need to add your own error checking BEFORE
    //the prepared statement is built and executed.

    //Now, we need to check if the supplied username already exists.

    //Construct the SQL statement and prepare it.
    $sqlUsername = "SELECT COUNT(username) AS num FROM users WHERE username = :username";
    $stmt = $pdo->prepare( $sqlUsername);

    //Bind the provided username to our prepared statement.
    $stmt->bindValue(':username', $username);

    //Execute.
    $stmt->execute();

    //Fetch the row.
    $row = $stmt->fetch(PDO::FETCH_ASSOC);

    //If the provided username already exists - display error.
    //TO ADD - Your own method of handling this error. For example purposes,
    //I'm just going to kill the script completely, as error handling is outside
    //the scope of this tutorial.
    if($row['num'] > 0){
        die('That username already exists!');
    }

    //Hash the password as we do NOT want to store our passwords in plain text.
    $passwordHash = password_hash($password, PASSWORD_BCRYPT, array("cost" => 12));

    //Prepare our INSERT statement.
    //Remember: We are inserting a new row into our users table.
     $sqlUsername = "INSERT INTO users (username, password) VALUES (:username, :password)";
    $stmt = $pdo->prepare( $sqlUsername);

    //Bind our variables.
    $stmt->bindValue(':username', $username);
    $stmt->bindValue(':password', $passwordHash);

    //Execute the statement and insert the new account.
    $result = $stmt->execute();

    //If the signup process is successful.
    if($result){
        //do something here
        echo 'Thank you for registering with our website.';
    }

}
?>