sql - 进行递归自联接的最简单方法？

在SQL Server中进行递归自联接的最简单方法是什么？我有一个这样的表:

PersonID | Initials | ParentID
1          CJ         NULL
2          EB         1
3          MB         1
4          SW         2
5          YT         NULL
6          IS         5

而且我希望能够获得仅与从特定人员开始的层次结构相关的记录。因此，如果我通过PersonID = 1请求CJ的层次结构，则会得到:

PersonID | Initials | ParentID
1          CJ         NULL
2          EB         1
3          MB         1
4          SW         2

对于EB，我会得到:

PersonID | Initials | ParentID
2          EB         1
4          SW         2

除了基于一堆联接的固定深度响应之外，我对此深感困惑。这样做会发生，因为我们没有很多级别，但我想正确地做。

谢谢!克里斯。

最佳答案

WITH    q AS
        (
        SELECT  *
        FROM    mytable
        WHERE   ParentID IS NULL -- this condition defines the ultimate ancestors in your chain, change it as appropriate
        UNION ALL
        SELECT  m.*
        FROM    mytable m
        JOIN    q
        ON      m.parentID = q.PersonID
        )
SELECT  *
FROM    q

通过添加排序条件，可以保留树的顺序:

WITH    q AS
        (
        SELECT  m.*, CAST(ROW_NUMBER() OVER (ORDER BY m.PersonId) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN AS bc
        FROM    mytable m
        WHERE   ParentID IS NULL
        UNION ALL
        SELECT  m.*,  q.bc + '.' + CAST(ROW_NUMBER() OVER (PARTITION BY m.ParentID ORDER BY m.PersonID) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN
        FROM    mytable m
        JOIN    q
        ON      m.parentID = q.PersonID
        )
SELECT  *
FROM    q
ORDER BY
        bc

通过更改ORDER BY条件，您可以更改 sibling 的顺序。