$user =  $DB->select('users', array('username','=','tomek')) or die(mysql_error());

class DB {
            private $_pdo,
            $_query,
            $_error = false,
            $_results,
            $_count = 0;


public static function getInstance() {
        if(!isset(self::$_instance)) {
            self::$_instance = new DB();
        }
        return self::$_instance;
    }

public function action($action, $table, $where = array()) {
        if (count($where) == 3) {
            $operators = array('=','>','<','>=','<=',);

            $field    = $where[0];
            $operator = $where[1];
            $value    = $where[2];

            if (in_array($operator, $operators)){
                $sql = "{$action} FROM {$table} WHERE {$field} {$operator} ?";
            }
        }
        return false;
    }
public function get($table, $where){
        return $this->action('SELECT *', $table, $where);
    }