递归函数取子集

CREATE DEFINER=`root`@`%` FUNCTION `GET_CHILD_COMMENT_STR`(id VARCHAR(50)) RETURNS longtext CHARSET utf8mb4
    SQL SECURITY INVOKER
BEGIN
  DECLARE r LONGTEXT default ''; 
    set r = (SELECT GROUP_CONCAT(PICK_COMMENT_ID) FROM (

        SELECT T1.PICK_COMMENT_ID,

        IF(FIND_IN_SET(REPLY_PICK_COMMENT_ID, @PIDS) > 0, @PIDS := CONCAT(@PIDS, ',', PICK_COMMENT_ID), 0) AS ISCHILD

        FROM (

        SELECT PICK_COMMENT_ID,REPLY_PICK_COMMENT_ID FROM APP_PICK_COMMENT T WHERE T.STATUS = '0' ORDER BY T.REPLY_PICK_COMMENT_ID, T.PICK_COMMENT_ID

        ) T1,

        (SELECT @PIDS := id) T2

        ) T3 WHERE ISCHILD != 0);
RETURN r;
END