T/SQL 中的递归子/父查询 [英] Recursive Child/Parent queries in T/SQL
问题描述
我在 Microsoft SQL Server 2008 中使用 T/SQL
I am using T/SQL in Microsoft SQL Server 2008
我有一张桌子
CREATE TABLE [TestTable](
[CHILD] [int] NOT NULL,
[PARENT] [int] NOT NULL
) ON [PRIMARY]
GO
这些是定义父子层次关系的一些值
These are some values which define a parent child hierarchial relationship
CHILD PARENT
1 2
2 0
3 1
4 2
5 0
从视觉上看,这张桌子是这样的
Visually, this table looks like this
0
2
1
3
4
5
理想情况下,我希望值显示如下(其中右侧栏表示世代)
I would ideally like the values to be shown as follows (where the right hand column indicates the generation)
CHILD GENERATION
0 0
2 1
1 2
3 3
4 2
5 1
我的 T/SQL 代码如下
My T/SQL code looks like this
with n(CHILD, PARENT, GENERATION) as (
select CHILD, PARENT,1 as GENERATION from TestTable
where PARENT=0
union all
select nplus1.CHILD, nplus1.PARENT, GENERATION+1 from TestTable as nplus1, n
where nplus1.PARENT=n.CHILD
)
select CHILD,GENERATION from n
然而它不起作用!
它回来了
CHILD GENERATION
2 1
5 1
1 2
4 2
3 3
它具有正确的生成,但排序顺序错误!有没有人有任何想法如何解决这个问题?
It has the right generation, but the wrong sort order! Does anyone have any ideas how to solve this?
谢谢!
推荐答案
你需要你的递归来构建一些可以在最后排序的东西:
You'll need your recursion to also build something that can be sorted by at the end:
declare @t TABLE (
[CHILD] [int] NOT NULL,
[PARENT] [int] NOT NULL
)
insert @t values
( 0, -1), -- I added this
( 1, 2 ),
( 2, 0 ),
( 3, 1 ),
( 4, 2 ),
( 5, 0 )
(注意我添加了一个真正的根元素)
(note I have added a true root element)
;with n(CHILD, PARENT, GENERATION, hierarchy) as (
select CHILD, PARENT,0, CAST(CHILD as nvarchar) as GENERATION from @t
where PARENT=-1
union all
select nplus1.CHILD, nplus1.PARENT, GENERATION+1,
cast(n.hierarchy + '.' + CAST(nplus1.child as nvarchar) as nvarchar)
from
@t as nplus1 inner join n on nplus1.PARENT=n.CHILD
)
select CHILD,GENERATION
from n
order by hierarchy
返回
CHILD GENERATION
----------- -----------
0 0
2 1
1 2
3 3
4 2
5 1
包括用于说明的 hierarchy
:
CHILD GENERATION hierarchy
----------- ----------- ------------------------------
0 0 0
2 1 0.2
1 2 0.2.1
3 3 0.2.1.3
4 2 0.2.4
5 1 0.5
根据您的 id 有多大,您可能需要使用零进行左填充才能正确排序.
Depending on how big your ids get, you might have to do stuff with left-padding with zeroes to get the sorting right.
请注意,SQL 2008 有一个内置的 hierarchy
类型来处理这种事情......
Note that SQL 2008 has a built-in hierarchy
type for this kind of thing...
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