formRegistar.php

<?php
#1 Confirmar as passwords
#2 Verificar se username já existe
if(isset($_GET['register'])){
    #Se a psw for igual à confirmação
    if($_GET['psw']==$_GET['pswRepeat']){
        #As passwords combinam
        #Testar se o username já existe
        require_once("../connection.php");
        $table="users";
        $username=addslashes($_GET['username']);
        $sql="SELECT id FROM $table WHERE username = '$username'";
        $query=mysqli_query($connect, $sql);
        $total=mysqli_num_rows($query);
        if($total == 0){
           #Posso registar
           $table="users";
           $sql="INSERT INTO $table (username) VALUES ('$username')";
           mysqli_query($connect, $sql);
            $idUser=mysqli_insert_id($connect);
           
            $table="passwords";
            $psw=addslashes($_GET['psw']);
            $sql="INSERT INTO $table (idUser, psw) VALUES ($idUser,'$psw')";
            mysqli_query($connect, $sql);
           
            $table="users_privilegios";
            $sql="INSERT INTO $table (idUser, idPrivilegio, idOperador) VALUES ($idUser, 4, $idUser)";
            mysqli_query($connect, $sql);
           
            $table="pessoas";
            $firstName=addslashes($_GET['firstName']);
            $lastName=addslashes($_GET['lastName']);
            $sql="INSERT INTO $table (firstName, lastName, idUser) VALUES ('$firstName', '$lastName', $idUser)";
            mysqli_query($connect, $sql);
            // sucesso
            $path="enviarEmailRegisto.php?username=$username";
        } else {
            #Não posso registar
            $path="?userRepetido";
        }
    } else {
        #As passwords não cobinam
        $path="?passwordProblem";
    }
    header("Location:$path");
}


?> 

   <form class="user">
    <div class="form-group row">
        <div class="col-sm-6 mb-3 mb-sm-0"><input class="form-control form-control-user" type="text" id="exampleFirstName" placeholder="First Name" name="firstName"></div>
        <div class="col-sm-6"><input class="form-control form-control-user" type="text" id="exampleFirstName" placeholder="Last Name" name="lastName"></div>
    </div>
    <div class="form-group"><input class="form-control form-control-user" type="email" id="exampleInputEmail" aria-describedby="emailHelp" placeholder="Email Address" name="username"></div>
    <div class="form-group row">
        <div class="col-sm-6 mb-3 mb-sm-0"><input class="form-control form-control-user" type="password" id="examplePasswordInput" placeholder="Password" name="psw"></div>
        <div class="col-sm-6"><input class="form-control form-control-user" type="password" id="exampleRepeatPasswordInput" placeholder="Repeat Password" name="pswRepeat"></div>
    </div><button class="btn btn-primary btn-block text-white btn-user" type="submit" name="register">Register Account</button>
    <hr><a class="btn btn-primary btn-block text-white btn-google btn-user" role="button"><i class="fab fa-google"></i>&nbsp; Register with Google</a><a class="btn btn-primary btn-block text-white btn-facebook btn-user" role="button"><i class="fab fa-facebook-f"></i>&nbsp; Register with Facebook</a>
    <hr>
</form>