I have a question about finding what amounts to the "head" of a "linked list" and using this to populate a column in a query. More specifically, I have a table which has two columns of numbers... a child column and a parent column like this:
Table: ParentChild
Child Parent
1000 500
1001 500
1002 501
1003 1001
etc
I would like to create a query that will list numbers in one column and list the ultimate parent in another column. To make it more interesting, if a number has no parent, I want it to list itself. So, in this example, I might have the following results:
Query: NumberParent
Number Parent
500 500 <== note that 500 is not listed as a child
501 501
1000 500
1001 500
1002 501
1003 500 <== note it took the grandparent
2000 2000 <== note that 2000 is not in the ParentChild table at all
etc
Is this possible to do in a SQL Query in Access? I am using Access 2000. I'm doing it now by exporting the ParentChild data into excel, doing what I need done there and reimporting it, but it sure seems like I should be able to do this another way!
If it is not possible, is there another (better) way to do this in Access? I've not used modules or forms or reports, so don't know what is possible there.
Thanks in advance!
Steve
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Oops.. couple of last minute small corrections:
--------------------------
Public Function GetParent ( ChildField As String ) As String
'
Dim LastParent As String: LastParent = Child
Dim ThisParent As String: ThisParent = Child
Do Until ThisParent = ""
ThisParent = DLookup ( MyTable, ThisParent, ParentField )
If ThisParent <> "" Then LastParent = ThisParent
Loop
GetParent = LastParent
'
End Function
--------------------------
Yes, that looks like exactly what I'm looking for! Where do I put the function? In the query? Or does it go in another section (I'd guess module. Is that the equivalent of a stored procedure in SQL?) I'm looking through the MS Access documentation now, but for some reason I find it hit and miss in its usefulleness.
Business Accounts
Answer for Membership
by: wsh2Posted on 2007-06-22 at 09:38:06ID: 19342766
This is to get you started. I am not at my computer right now, so it is Air Coded which means you may have to fix errors: You didn't specify field types so I played it safe and made them Strings.
--------------------------
Public Function GetParent ( ChildField As String ) As String
'
Dim LastParent: LastParent = Child
Dim ThisParent: ThisParent = Child
Do Until ThisParent = 0
ThisParent = DLookup ( MyTable, ThisParent, ParentField )
If ThisParent <> "" Then LastParent = ThisParent
Loop
GetParent = LastParent
'
End Function
--------------------------
Usage:
SELECT ChildField, GetParent(ChildField)
FROM MyTable
End Function