PDO connect

<?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();
}
?>

$host     = "localhost";//Ip of database, in this case my host machine    
$user     = "root";	//Username to use
$pass     = "qwerty";//Password for that user
$dbname   = "DB";//Name of the database

try {
    $connection = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
    $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

}catch(PDOException $e)
{
  echo $e->getMessage();                         
}

<?php 
  
	$pdo = new PDO('mysql:host=localhost;
  				dbname=the_name_of_your_databe,
  				'username', 
                'password'');
# by default your username is root 
# if you don't have a password don't fill in it

#(optional) : 
	$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
	$pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);

?>

public static function connexionBDD()
    {
        $base = null;

        try {
            $base = new PDO('mysql:host=' . MYSQL_HOSTNAME . '; dbname=' . MYSQL_DATABASE . '', MYSQL_USERNAME, MYSQL_PASSWORD);
        } catch (exception $e) {
            die('Erreur ' . $e->getMessage());
        }

        return $base;
    }

<?php
$db = new PDO('mysql:host=myhost;dbname=mydb', 'login', 'password');