SQL Server 2008：递归迭代方法

Question

想象一下名为Group的表，每个组都可以拥有'子'组，只要它们的级别较低。因此Group and childGroup表之间存在一对多的关系。

many-to-many和Group之间也存在Items关系，因此Groups_Items用于保存每个表的FK。

我需要写一个查询，其中given Group key，find all its child组，all the childs of child groups和the customers belonging to those found groups。

我知道它需要是某种类型的递归查询，但我不知道如何在SQL中完成此操作。以下是所讨论表格的结构：

所以，如果我在上表中设置了这些数据：

查询是查找For Group 1, find Its customers, Its Child groups (and their Childs) and all their customers，输出应为：

<Group> 1
    <customer> 1
    <customer> 2
    <Group> 2
        <customer> 2
        <Group> 3
        <Group> 4

有人可以告诉我这是怎么做到的吗？谢谢

Answer 1

我希望我理解你的问题

;WITH Hierarchy (GroupID,ID,  ParentID
               ,hLevel
               ) AS
(
   -- Base case
   (
   Select  [Parent Key] as GroupID,NULL,NULL,0
   FROM Tree
   where [Parent Key]=1
   UNION
   SELECT
      [Child Key] as GroupID,
      [Child Key] as ID,
      [Parent Key] as ParentID
      ,1 as hLevel
   FROM Tree
   where [Parent Key]=1
   ) 

   UNION ALL

   -- Recursive step
   SELECT
      e.[Child Key] as GroupID,
      e.[Child Key],
      e.[Parent Key]
     ,eh.hLevel + 1
   FROM tree e
      INNER JOIN Hierarchy eh ON
         e.[Parent Key] = eh.ID
)


Select Distinct h.GroupID, c.Name,h.ParentID as ParentGroupID
from Hierarchy h
left join test c on h.GroupID=c.ID

较旧的尝试将是

Declare @Parent int
Declare @count int
Select @Parent=??

Select cast(ID as Int) as ID
into #tmp
from Tabelle where ParentID=@Parent

select @Count=0
While @Count<(Select Count(*) from #tmp)
   begin
   Select @Count=(Select Count(*) from #tmp)
   insert into #tmp Select Cast(ID as int) from Tabelle where ParentID in (Select ID from #tmp) and ID not in (Select ID from #tmp)
   end
Select * from #tmp
Drop table #tmp