Record duplication issue

Question

I am currently having an issue linking two tables in a report.  When I generate the report, the records in the detail section become duplicated.  To further explain, in one table I am looking for item numbers, transaction date and transaction quantity. 
In the next, I am looking for item numbers, transaction dates, and shipment quantities.
In the last I am retrieving item numbers and descriptions. 
The only fields that seem to be consistent between tables are the item numbers, so I am joining on that basis.
However, what ends up happening is this:
Item #   Date       Trans Qty      Date        Ship Qty
1001 (Grouping)
              5/12/09     49000       5/20/09     20000
              5/12/09     49000       5/28/09     12000
              6/1/09       30000       5/20/09     20000
              6/1/09       30000       5/28/09     12000
2001 (Group)
              5/12/09     20000       5/5/09       20000
              5/12/09     20000       5/19/09     12000
              5/12/09     20000       6/5/09       15000
If you know why this is happening, or better yet, a way to fix it, I would greatly appreciate your help.

Answer 1

It is happening because the item number appears multiple times in one or more of the "left tables" in the join.
How to fix it depends on what you are trying to accomplish.
If you are trying to match something like Order Details to Shipment Details against those orders, you'll need an order and line number in your Shipment Details file that reference the same fields in the Order Detail file.
If you are just looking for total ordered vs total shipped, you'll need to aggregate the ordered and shipped quantities by item BEFORE doing the join.  In SQL it would look something like this (MS SQL):
select isnull(a.item_no, b.item_no) as Item_no,
   isnull(a.ordered_qty,0) as ordered_qty,
   isnull(b.shipped_qty, 0) as shipped_qty
from (
    select item_no, sum(ordered_qty) as ordered_qty
    from Order_Details
    where date between {?start date} and {?end date}
    group by item_no
) a
full outer join (
    select item_no, sum(shipped_qty) as shipped_qty
    from Shipment_Details
    where date between {?start date} and {?end date}
    group by item_no
) b
on a.item_no = b.item_no
HTH,
Carl