$conn = new mysqli code example

Example 1: how to connect pdo php database

<?php
$servername = "localhost";
$username = "username";
$password = "password";

try {
  $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
  // set the PDO error mode to exception
  $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  echo "Connected successfully";
} catch(PDOException $e) {
  echo "Connection failed: " . $e->getMessage();
}
?>

Example 2: mysqli database

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "test");

/* Vérification de la connexion */
if (mysqli_connect_errno()) {
    printf("Échec de la connexion : %s\n", mysqli_connect_error());
    exit();
}

/* Retourne le nom de la base de données courante */
if ($result = $mysqli->query("SELECT DATABASE()")) {
    $row = $result->fetch_row();
    printf("La base de données courante est %s.\n", $row[0]);
    $result->close();
}

/* Change la base de données en "world" */
$mysqli->select_db("world");

/* Retourne le nom de la base de données courante */
if ($result = $mysqli->query("SELECT DATABASE()")) {
    $row = $result->fetch_row();
    printf("La base de données courante est %s.\n", $row[0]);
    $result->close();
}

$mysqli->close();
?>