Mysql & Php Database connection error - php

Question

When ever I use php to connect to my database I get a sudden error saying "database connection failed" is there anyway to fix this its for a login and register screen. Thanks to anyone who help...
<?php
$connection = mysqli_connect('localhost', 'root','','test');
if (!$connection){
die("Database Connection Failed" . mysqli_error($connection));
}
$select_db = mysqli_select_db($connection, 'test');
if (!$select_db){
die("Database Selection Failed" . mysqli_error($connection));
}
<?php
//
require('database.php');
$connection = mysqli_connect('localhost', 'root','','test');
// If the values are posted, insert them into the database.
if (isset($_POST['Register'])){
$username = $_POST['username'];
$email = $_POST['email'];
$password = $_POST['password'];
$query = "INSERT INTO `user` (username, email, password) VALUES ('$username', '$email', '$password')";
//echo $query;
$result=mysqli_query($connection,$query);
if($result){
$smsg = "User Created Successfully.";
}else{
$fmsg ="User Registration Failed";
}
}
?>

Answer 1

Connection to a database with php requires 4 parameters (host, data base user, password, data base name, passwd), it's better nowadays to use db object instead of procedural "old" behaviour:
function connection(){
try{
//host, user, passwd, DB name)
$mysqli = new mysqli("localhost", $dbUser, $passwd, $dbName);
if (!$mysqli->set_charset("utf8")) $msg = "error charset mySQLi"; else $msg = "Set UTF-8 ok";
return $mysqli;
}
catch (Exception $mysqlin){
echo "Error stablishing connection with database ".$mysqlin->getMessage();
}
}
then you can connect easily as follows:
$sql = "SELECT * FROM users;";
if(!$result = connection()->query($sql)) echo "db query error"; else "query ok";
$rs = mysqli_fetch_assoc($result);
//do whatever and, to get next line of results:
if($rs!=''){
$rs = mysqli_fetch_assoc($result);
}
So you get a row of the results on $rs[] array.
EDIT: You'll need to apply security, this is a simple connection without regarding on it. Check mysqli bind params on php official webpage for it:
http://php.net/manual/en/mysqli-stmt.bind-param.php
Hope it helps