最简单的递归自联接方式？

Question

在SQL Server中执行递归自联接的最简单方法是什么？我有这样一张桌子:

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特定人员开始的层次结构相关的记录.所以,如果我通过PersonID = 1请求CJ的层次结构,我会得到:

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

我有点卡住这个可以想不出怎么做除了基于一堆连接的固定深度响应.这会发生,因为我们不会有很多级别,但我想做得恰到好处.

谢谢!克里斯.

Answer 1

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,您可以保留树顺序:

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,您可以更改兄弟姐妹的顺序.

Answer 2

使用CTE你可以这样做

DECLARE @Table TABLE(
        PersonID INT,
        Initials VARCHAR(20),
        ParentID INT
)

INSERT INTO @Table SELECT     1,'CJ',NULL
INSERT INTO @Table SELECT     2,'EB',1
INSERT INTO @Table SELECT     3,'MB',1
INSERT INTO @Table SELECT     4,'SW',2
INSERT INTO @Table SELECT     5,'YT',NULL
INSERT INTO @Table SELECT     6,'IS',5

DECLARE @PersonID INT

SELECT @PersonID = 1

;WITH Selects AS (
        SELECT *
        FROM    @Table
        WHERE   PersonID = @PersonID
        UNION ALL
        SELECT  t.*
        FROM    @Table t INNER JOIN
                Selects s ON t.ParentID = s.PersonID
)
SELECT  *
FROm    Selects

Answer 3

对大表进行了更改的 Quassnoi 查询。孩子多于 10 岁的父母：将 row_number() 格式化为 str(5)

与 q AS 
        (
        SELECT m.*, CAST(str(ROW_NUMBER() OVER (ORDER BY m.ordernum),5) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN AS bc
        从#tm
        哪里 ParentID =0
        联合所有
        选择 m.*, q.bc + '.' + str(ROW_NUMBER() OVER (PARTITION BY m.ParentID ORDER BY m.ordernum),5) COLLATE Latin1_General_BIN
        从#tm
        加入q
        ON m.parentID = q.DBID
        )
选择 *
从 q
订购者
        公元前