多父母的所有孩子的 CTE答案

【问题标题】：CTE for all Child for Multiple parent多父母的所有孩子的 CTE
【发布时间】：2016-08-25 06:03:52
【问题描述】：

我有一个父子关系表如下图：

ContractID        ContractIdRef
----------        -------------
 1                 null
 2                 1
 3                 1
 4                 2
 5                 4
 10                null
 11                10
 12                11
 15                null
 16                12

我想要如下结果：

 ContractID        ContractIdRef    rw
-----------        --------------   ---
 1                 null             1
 2                 1                1
 3                 1                1
 4                 2                1
 5                 4                1
 10                null             10
 11                10               10
 12                11               10
 15                null             15
 16                12               10

在上面的结果中，我想指定每一行的父级。
谢谢

【问题讨论】：

标签： sql recursion common-table-expression

【解决方案1】：

正如你在标签中提到的那样，Comman Table Expression 是要走的路

;WITH REC_CTE 
     AS (SELECT [contractid], 
                [ContractIdRef], 
                [contractid] AS rw
         FROM   Yourtable
         WHERE  [contractidref] IS NULL 
         UNION ALL 
         SELECT T.[contractid], 
                T.[contractidref], 
                c.rw
         FROM   Yourtable AS T 
                INNER JOIN REC_CTE C 
                        ON T.[contractidref] = c.[contractid] 
         WHERE  T.[contractid] <> T.[contractidref]) 
SELECT [contractid], 
       [contractidref],
       rw
FROM   REC_CTE 
ORDER  BY [contractid]

演示

架构设置

If object_id('tempdb.dbo.#Yourtable') is not null
DROP table #Yourtable

CREATE TABLE #Yourtable
    ([ContractID] INT, [ContractIdRef] INT);

样本数据

INSERT INTO #Yourtable
    ([ContractID], [ContractIdRef])
VALUES
    ('1', NULL),
    ('2', '1'),
    ('3', '1'),
    ('4', '2'),
    ('5', '4'),
    ('10', NULL),
    ('11', '10'),
    ('12', '11'),
    ('15', NULL),
    ('16', '12');

查询

;WITH REC_CTE
     AS (SELECT [ContractID], 
                [ContractIdRef] as [ContractIdRef],
                [ContractID] AS rw 
         FROM   #Yourtable where [ContractIdRef] is null

         UNION ALL 
         SELECT T.[ContractID], 
                T.[ContractIdRef], 
                c.rw 
         FROM   #Yourtable  AS T 
                INNER JOIN REC_CTE c 
                        ON T.[ContractIdRef] = c.[ContractID] 
         WHERE  T.[ContractID] <> T.[ContractIdRef]) 
SELECT [ContractID], 
       [ContractIdRef],
       rw 
FROM   REC_CTE 
ORDER  BY [ContractID]

结果

+-----------+-------------+----+
|ContractID |ContractIdRef| rw |
+-----------+-------------+----+
|1          |NULL         | 1  |
|2          |1            | 1  |
|3          |1            | 1  |
|4          |2            | 1  |
|5          |4            | 1  |
|10         |NULL         | 10 |
|11         |10           | 10 |
|12         |11           | 10 |
|15         |NULL         | 15 |
|16         |12           | 10 |
+-----------+-------------+----+

【讨论】：

【解决方案2】：

with Q as(
  select ContractID, ContractIdRef, ContractID as root
    from childs
   where ContractIdRef is null
 union all
  select C.ContractID, C.ContractIdRef, Q.root
    from Q, childs C
   where C.ContractIdRef=Q.ContractID
)
select * from Q
 order by ContractID

在 MS SQL 2014 上测试。

对于 Postgresql 需要在 'with' 之后添加单词 'recursive'。 Test on sqlfiddle.com

对于 Oracle，第一行写成with Q(ContractID,ContractIdRef,root)。

【讨论】：