Question

Imagine a Table named Group, each group can have ‘child’ groups as long as they’re of lower ‘level’. So there is one-to-many relationship between Group and childGroup table.

There is also a many-to-many relation between Group and Items so Groups_Items is used to hold the FK of each table.

I need to write a query where for a given Group key, i should find all its child groups, all the childs of child groups, and all the customers belonging to those found groups.

I know it needs to be a recursive query of some sort but i have no idea how this can be done in SQL. Below is the structure of the tables discussed:

so if i had these data set in the above tables:

And the query was to find For Group 1, find Its customers, Its Child groups (and their Childs) and all their customers, the output should be:

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

Can someone please show me how this can be done? thanks

Answer 1

I hope I understood your question

;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

an older attempt would be

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