proses_daftar.php

<?php
session_start();
$conn = new mysqli('localhost','a','q','b_login');

$nama = $_POST['nama_lengkap'];
$email = $_POST['email'];
$username = $_POST['username'];
$password = base64_encode($_POST['password']);

$query = $conn->query("SELECT username from user WHERE username = '$username' ");
$res = $query->fetch_assoc();

if(count($res) >= 1){
    echo "<p style='color:red'>Username Sudah Di Gunakan !!!</p>";
    echo "<a href='daftar.php'> << Kembali </a>";
}
else{
    $impan = $conn->query("INSERT INTO user VALUES(null, '$nama', '$email', '$username', '$password')");
    $_SESSION['username'] = $username;
    header('location:home.php');
}