sql-server - SQL Server 2008：递归迭代操作方法

Question

想象一个名为 的表Group，每个组都可以有“子”组，只要它们的“级别”较低。所以表之间是一对多的关系Group and childGroup。

和之间还有一个many-to-many关系Group，Items所以Groups_Items用来保存每个表的FK。

我需要编写一个查询，对于 a given Group key，我应该对、 和 all进行find all its child分组。all the childs of child groupsthe customers belonging to those found groups

我知道它需要是某种递归查询，但我不知道如何在 SQL 中完成。以下是讨论的表的结构：

所以如果我在上表中有这些数据集：

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

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

有人可以告诉我如何做到这一点吗？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