Hi all, I wrote a design doc about Support User-Defined Table Function (UDTF). If you are interested, please click the link: https://docs.google.com/document/d/1-dVfGeIfXBpVKtoWmPye11BO7Wn-sQTqBMemKf9zJ4k/edit#heading=h.rxomr7gsib44
Looking forward to your suggestions. Thanks, gaoxiaoqing
