mysql db connection in php

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# MySql improved
2<?php
3    $mysqli = new mysqli("localhost", "username", "password", "dbname");
4	$result = $mysqli->query("SELECT lastname FROM employees");
5?>
6# Connection with PDO
7<?php
8    $myPDO = new PDO('mysql:host=localhost;dbname=dbname', 'username', 'password');
9	$result = $myPDO->query("SELECT lastname FROM employees");
10?>
11# With PHP legacy functions:
12<?php
13    mysql_connect('localhost','username','password');
14    mysql_select_db("dbname");
15	$result = mysql_query('SELECT lastname FROM employees');
16?>

1<?php
2
3$hostName = 'localhost';
4$userNmame = 'root';
5$password = '';
6$dbname = 'topproduct';
7$db_name = "mysql:host=$hostName;dbname=$dbname";
8$conn = new PDO($db_name,$userNmame,$password);
9
10if(!$conn){
11    echo 'Error database connection';    
12}
13

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

1
2<?php
3$mysqli = new mysqli("localhost","my_user","my_password","my_db");
4
5// Check connection
6if ($mysqli -> connect_errno) {
7
8  echo "Failed to connect to MySQL: " . $mysqli -> connect_error;
9  
10  exit();
11
12  }
13?>