how to connect database with mysql, MySQLi , pdo in php

Mysql database connection

    $database_host = 'localhost'; // database host name
    // if using port then add port $database_host = 'localhost:3036';  
    $database_user = 'database_user'; // database user name
    $database_pass = 'database_password'; // database user password
	
	// connect with database
    $database_conn = mysql_connect($database_host, $database_user, $database_pass);
	
	// check database connection 
    if(! $database_conn )
    {
		// error in database connection
		die('Could not connect to database : ' . mysql_error()); 
    } 
	// connected to database
    echo 'Connected successfully with database'; 
	
	// close connection with Mysql database
    mysql_close($database_conn); 
	

MySQLi Object-Oriented database connection

    $database_host = 'localhost'; // database host name
    // if using port then add port $database_host = 'localhost:3036';  
    $database_user = 'database_user'; // database user name
    $database_pass = 'database_password'; // database user password

	// connect with database
	$database_conn = new mysqli($database_host, $database_user, $database_pass);

	// check database connection 
	if ($database_conn->connect_error) 
	{	
		// error in database connection
		die("Could not connect to database : " . $database_conn->connect_error);
	} 
	
	// connected to database
	echo 'Connected successfully with database';
	
	// close connection with MySQLi database
	$database_conn->close();

MySQLi Procedural database connection

    $database_host = 'localhost'; // database host name
    // if using port then add port $database_host = 'localhost:3036';  
    $database_user = 'database_user'; // database user name
    $database_pass = 'database_password'; // database user password

	// connect with database
	$database_conn = mysqli_connect($database_host, $database_user, $database_pass);

	// check database connection 
	if (!$database_conn) 
	{
		// error in database connection
		die("Could not connect to database : " . mysqli_connect_error());
	}
	
	// connected to database
	echo 'Connected successfully with database';
	
	// close connection with MySQLi Procedural
	mysqli_close($database_conn);

PDO database connection

    $database_host = 'localhost'; // database host name    
    $database_user = 'database_user'; // database user name
    $database_pass = 'database_password'; // database user password
	$database_name = 'your_database_name'; // database name

	try 
	{
		$database_conn = new PDO("mysql:host=$database_host;dbname=$database_name", $database_user, $database_pass);
		// if using port then use port id in PDO  
		//$database_conn = new PDO('mysql:host=$database_host;port=5432;dbname=$database_name', $database_user, $database_pass);
		
		// exception for PDO connection error
		$database_conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
		
		// connected to database
		echo 'Connected successfully with database';
	}
	catch(PDOException $exception)
	{
		// error in database connection
		echo "Could not connect to database : " . $exception->getMessage(); // exception
	}
	
	// close connection with PDO
	$database_conn = null;