Check mysqli Insert Query excuted ok and display message and send email

I am creating a registration form for a project, nothing secure or advanced, i am still fairly new to php etc.

I insert the data needed to into a login table and a customer tbl, the data inserts fine. But i cant get the code to check that its worked and fire off a an email and display a message to the user.

I have tried using a value retrieved from the database which would only be there is the user registered successfuly.

if($userID != null)
            {
                $msg1 = "Thank You! you are now registered, please check your email for a verification link to verify your new account! ";
                $col1 = "green";
                //require_once "Mail.php";
                require_once "inc/email.php";

            }

I have also tried this

if($query)
            {
                $msg1 = "Thank You! you are now registered, please check your email for a verification link to verify your new account! ";
                $col1 = "green";
                //require_once "Mail.php";
                require_once "inc/email.php";

        }

Thanks,