<?php
require_once 'config.php'; // Database setting constants [DB_HOST,  DB_NAME, DB_USERNAME, DB_PASSWORD]
class dbHelper {
private $db;
private $err;
function __construct() {
    $dsn = 'mysql:host='.DB_HOST.';dbname='.DB_NAME.';charset=utf8';
    try {
        $this->db = new PDO($dsn, DB_USERNAME, DB_PASSWORD, array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
    } catch (PDOException $e) {
        $response["status"] = "error";
        $response["message"] = 'Connection failed: ' . $e->getMessage();
        $response["data"] = null;
        exit;
    }
}


function select($table, $where){
    try{
        $a = array();
        $w = "";
        foreach ($where as $key => $value) {
            $w .= " and " .$key. " like :".$key;
            $a[":".$key] = $value;
        }
        $stmt = $this->db->prepare("select * from ".$table." where 1=1 ". $w);
        $stmt->execute($a);
        $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
        if(count($rows)<=0){
            $response["status"] = "warning";
            $response["message"] = "No data found.";
        }else{
            $response["status"] = "success";
            $response["message"] = "Data selected from database";
        }
            $response["data"] = $rows;
    }catch(PDOException $e){
        $response["status"] = "error";
        $response["message"] = 'Select Failed: ' .$e->getMessage();
        $response["data"] = null;
    }
    return $response;
}
}

<?php
     /**
     * Database configuration
 */
define('DB_USERNAME', 'root');
define('DB_PASSWORD', '');
define('DB_HOST', 'localhost');
define('DB_NAME', 'database1');

?>

<?php
require_once 'dbHelper.php';
$db = new dbHelper();

$rows = $db->select("customers_php",array());
print_r(json_encode($rows,JSON_NUMERIC_CHECK));
?>

if($db_name == 'database1')
{
    //#----------open database connection --------------------> TESTING
    $db_host = "localhost";
    $db_user = "root";
    $db_password = "";
    $db_name = "database1";
}

if($db_name == 'database2')
{
    //#----------open database connection --------------------> TESTING
    $db_host = "localhost";
    $db_user = "root";
    $db_password = "";
    $db_name = "database2";
}

<?php
require_once 'dbHelper.php';
$db = new dbHelper();

//function select($dbname, $table, $where)......................

$rows = $db->select("database1","customers_php",array());
print_r(json_encode($rows,JSON_NUMERIC_CHECK));
?>