Sql 递归CTE以查找所有项的所有祖先
我有一个简单的层次结构,需要能够生成一个表,将表中的每个项与其所有祖先项相匹配。(大写强调这不是重复的问题!) 这是一张桌子:Sql 递归CTE以查找所有项的所有祖先,sql,recursion,sql-server-2012,hierarchy,common-table-expression,Sql,Recursion,Sql Server 2012,Hierarchy,Common Table Expression,我有一个简单的层次结构,需要能够生成一个表,将表中的每个项与其所有祖先项相匹配。(大写强调这不是重复的问题!) 这是一张桌子: Select Item='A', Parent=null into Items union Select Item='B', Parent='A' union Select Item='C', Parent='A' union Select Item='D', Parent='B' union Select Item='E', Parent='B' union
Select Item='A', Parent=null into Items union
Select Item='B', Parent='A' union
Select Item='C', Parent='A' union
Select Item='D', Parent='B' union
Select Item='E', Parent='B' union
Select Item='F', Parent='C' union
Select Item='G', Parent='C' union
Select Item='H', Parent='D'
Go
。。。表示此层次结构的:
A
/ \
B C
/ \ / \
D E F G
/
H
所以B有一个祖先(A),H有三个祖先(D,B,A)。这是所需的输出:
Item | Ancestor
B | A
C | A
D | A
D | B
E | A
E | B
F | A
F | C
G | A
G | C
H | A
H | B
H | D
使用递归CTE,我能够找到任何一项的所有子体
Create Function ItemDescendants(@Item char) Returns @result Table(Item char) As Begin
; With AllDescendants as (
Select
Item,
Parent
From Items i
Where Item=@Item
UNION ALL
Select
i.Item,
i.Parent
from Items i
Join AllDescendants a on i.Parent=a.Item
)
Insert into @result (Item)
Select Item from AllDescendants
Where Item<>@Item;
Return;
End
Go
这是可行的,但如果我能用一个优雅的查询来完成它,我会非常高兴。似乎这应该是可能的-有什么想法吗?假设我理解正确,它应该像从叶节点向后递归一样简单(这很容易,因为表项只存储叶节点):
Select Item, Parent into #t From Items
Declare @Item char
Declare c Cursor for (Select Item from Items)
Open c
Fetch c into @Item
While (@@Fetch_Status=0) Begin
Insert into #t (Item, Ancestor) Select Item, @Item from dbo.ItemDescendants(@Item)
Fetch c into @Item
End
Close c
Deallocate c
Select Distinct
Item,
Ancestor
From #t
Where Parent is not null
Order by Item,Parent
Drop Table #t
;with AncestryTree as (
select Item, Parent
from Items
where Parent is not null
union all
select Items.Item, t.Parent
from AncestryTree t
join Items on t.Item = Items.Parent
)
select * from AncestryTree
order by Item, Parent