Do I need a php mysql connection in each function that uses database?

Create a config.php And add the code:

config.php:

$hostname = 'host';
$username = 'username';
$password = 'password';
$dbname   = 'dbname';

$conn = mysqli_connect($hostname, $username, $password) OR die('Unable to connect to database! Please try again later.');
mysqli_select_db($conn, $dbname);

Then in any file you wish to use mysql, add the following:

script2.php

<?php
require_once 'config.php';

mysqli_query($sqlApiAccess) or die('Error, insert query failed');
?>

To avoid creating a new database connection each time, we can use Singleton design pattern-

we need to have a database class- to handle the DB connection-

Database.class.php

<?php
        class Database
        {
            // Store the single instance of Database
            private static $m_pInstance;

            private $db_host='localhost';
            private $db_user = 'root';
            private $db_pass = '';
            private $db_name = 'databasename';

            // Private constructor to limit object instantiation to within the class
            private function __construct() 
            {
                mysql_connect($this->db_host,$this->db_user,$this->db_pass);
                mysql_select_db($this->db_name);
            }

            // Getter method for creating/returning the single instance of this class
            public static function getInstance()
            {
                if (!self::$m_pInstance)
                {
                    self::$m_pInstance = new Database();
                }
                return self::$m_pInstance;
            }

            public function query($query)
            {
               return mysql_query($query);
            }

         }
?>

& we can call it from other files-

other.php

<?php
       include 'singleton.php';
       $pDatabase = Database::getInstance();

       $result = $pDatabase->query('...');
?>