php mysql pdo connection

1<?php
2$servername = "localhost";
3$username = "username";
4$password = "password";
5$dbname = "myDB";
6
7// Create connection
8$conn= mysqli_connect($servername,$username,$password,$dbname);
9// Check connection
10if (!$conn) {
11  die("Connection failed: " . mysqli_connect_error());
12}
13echo "Connected Successfully.";
14?>

1<?php
2$servername = "localhost";
3$username = "username";
4$password = "password";
5
6try {
7    $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
8    // set the PDO error mode to exception
9    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
10    echo "Connected successfully";
11    }
12catch(PDOException $e)
13    {
14    echo "Connection failed: " . $e->getMessage();
15    }
16?>

1$host     = "localhost";//Ip of database, in this case my host machine    
2$user     = "root";	//Username to use
3$pass     = "qwerty";//Password for that user
4$dbname   = "DB";//Name of the database
5
6try {
7    $connection = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
8    $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
9
10}catch(PDOException $e)
11{
12  echo $e->getMessage();                         
13}

1public static function connexionBDD()
2    {
3        $base = null;
4
5        try {
6            $base = new PDO('mysql:host=' . MYSQL_HOSTNAME . '; dbname=' . MYSQL_DATABASE . '', MYSQL_USERNAME, MYSQL_PASSWORD);
7        } catch (exception $e) {
8            die('Erreur ' . $e->getMessage());
9        }
10
11        return $base;
12    }

1<?php
2$pdo = new PDO('mysql:host=localhost;dbname=databasename', 'username', 'password');
3?>
4

1<?php 
2  
3	$pdo = new PDO('mysql:host=localhost;
4  				dbname=the_name_of_your_databe,
5  				'username', 
6                'password'');
7# by default your username is root 
8# if you don't have a password don't fill in it
9
10#(optional) : 
11	$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
12	$pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);
13
14?>