使用SQL Server CTE返回所有父记录

Question

我有以下表类层次结构.

ClassID    ParentID
--------------------
PMM_00001  null
PMM_00010  PMM_00001
PMM_00110  PMM_00010
PMM_00020  PMM_00001
PMM_00220  PMM_00020

我希望得到以下结果.

ClassID    Class_Join
---------------------
PMM_00001  PMM_00001
PMM_00010  PMM_00001
PMM_00010  PMM_00010
PMM_00110  PMM_00001
PMM_00110  PMM_00010
PMM_00110  PMM_00110
PMM_00020  PMM_00001
PMM_00020  PMM_00020
PMM_00220  PMM_00001
PMM_00220  PMM_00020
PMM_00220  PMM_00220

我计划通过加入我的特征表来使用这些结果来获得继承的特征.在过去,我使用循环来正确设置数据,但我想使用CTE来获得这些结果.

这是我到目前为止所尝试的.

;WITH ClassHierarchy_CTE (ClassID, ClassID_Join)
AS
(
SELECT
    c.ClassID,
    c.ClassID
FROM
    ClassHierarchy AS h
WHERE
    h.ParentID IS NULL
UNION ALL
SELECT
    c.ClassID,
    h.ParentID
FROM
    ClassHierarchy AS h INNER JOIN ClassHierarchy_CTE
        ON
            h.ParentID = ClassHierarchy_CTE.ClassID
)
SELECT
    *
FROM
    ClassHierarchy_CTE
ORDER BY
    ClassID

我从中获得的结果只是沿着层次结构向下走,以获得完整的列表.我需要将引用返回到层次结构中的每个级别,以便我可以获得完整的特征列表.任何帮助表示赞赏!如果有更好的方法,我愿意接受建议.

Answer 1

看起来我接近这一切都错了.我缺少的概念是我需要向上移动层次结构,而不是向下移动(因为大多数文档/文章都在那里演示).所以这就是我做的.

CREATE TABLE hierarchy
(
  ClassID  nvarchar(100), ParentID nvarchar(100)
)

INSERT INTO hierarchy
( ClassID     ,           ParentID)
VALUES
( N'PMM_00001',      NULL    ),
( N'PMM_00010',      N'PMM_00001'),
( N'PMM_00110',      N'PMM_00010'),
( N'PMM_00020',      N'PMM_00001'),
( N'PMM_00220',      N'PMM_00020')

;WITH ClassHierarchy_CTE (ClassID, ClassID_Join, Level)
AS
(
SELECT
    ClassID,
    ClassID AS Join_Class,
    0
FROM
    hierarchy AS c
UNION ALL
SELECT
    cte.ClassID,
    h.ParentID,
    Level + 1
FROM
    hierarchy AS h INNER JOIN ClassHierarchy_CTE as cte
      ON
        h.ClassID = cte.ClassID_Join
)
SELECT
    *
FROM
    ClassHierarchy_CTE
WHERE
    ClassID_Join IS NOT NULL
ORDER BY
    ClassID,
    Level

返回...

CLASSID CLASSID_JOIN    LEVEL
---------------------------------
PMM_00001   PMM_00001   0
PMM_00010   PMM_00010   0
PMM_00010   PMM_00001   1
PMM_00020   PMM_00020   0
PMM_00020   PMM_00001   1
PMM_00110   PMM_00110   0
PMM_00110   PMM_00010   1
PMM_00110   PMM_00001   2
PMM_00220   PMM_00220   0
PMM_00220   PMM_00020   1
PMM_00220   PMM_00001   2

SQLfiddle供参考.