public function where($column, $operator, $value = null)
    {
        if (is_null($value)) {
            if (is_callable($operator)) {
                $this->where[] = [$column, 'func', $operator];
            } else {
                $this->where[] = [$column, '=', $operator];
            }
        } else {
            $this->where[] = [$column, $operator, $value];
        }

        return $this;
    }