SQL 樹 遞迴 查詢所有子節點

WITH T AS
(
SELECT CID,ParentID
    , 0 AS Level
    FROM SYS_Category
    WHERE CID = 8
     UNION ALL
    SELECT c.CID,c.ParentID, Level +1
    FROM SYS_Category c
    inner JOIN T t1
    ON c.ParentID=t1.CID
)
SELECT * FROM T;