private function getWhereString()
    {
        // If there are not where conditions, return empty
        if (!count($this->wheres)) {
            return 'WHERE 1=1 ';
        }

        // Create where named placeholders
        $wheres = array_map(function ($where) {
            return $where['table'] . '.' . $where['column'] . ' ' . $where['operator'] . ' :' . $where['table'] . $where['column'];
        }, $this->wheres);

        // String holder
        return 'WHERE 1 AND ' . implode(' AND ', $wheres);
    }