Using top clause in Access sub report

Question

I'm making a report in Access 2003 that contains a sub report of related records. Within the sub report, I want the top two records only. When I add "TOP 2" to the sub report's query, it seems to select the top two records before it filters on the link fields. How do I get the top two records of only those records that apply to the corresponding link field? Thanks.

Answer 1

I've got two suggestions:
1) Pass your master field (on the parent form) to the query as a parameter (you could reference a field on the parent form directly as well)
2) You could fake out rownumbers in Access and limit them to only rownum <= 2. E.g.,

SELECT o1.order_number, o1.order_date,
    (SELECT COUNT(*) FROM orders AS o2
        WHERE o2.order_date <= o1.order_date) AS RowNum
    FROM
        orders AS o1
    ORDER BY o1.order_date

(from http://groups.google.com/group/microsoft.public.access.queries/msg/ec562cbc51f03b6e?pli=1)
However, this kind of query might return an read only record set, so it might not be appropriated if you needed to do the same thing on a Form instead of a Report.

Answer 2

The sample query below is supposed to return a pair of most recent orders for each customer (instead of all orders):

select
    Order.ID,
    Order.Customer_ID,
    Order.PlacementDate
from
    Order
where
    Order.ID in 
        (
            select top 2
                RecentOrder.ID
            from
                Order as RecentOrder
            where
                RecentOrder.Customer_ID = Order.Customer_ID
            order by
                RecentOrder.PlacementDate Desc
        )

A query like this could be used in your sub-report to avoid using a temporary table.

CAVEAT EMPTOR: I did not test this sample query, and I don't know if this query would work for a report running against Jet database (we don't use Access to store data and we avoid Access reports like plague :-). But it should against SQL Server.

I also don't know how well it would perform in your case. As usual, it depends. :-)

BTW, speaking of performance and hacks. I would not consider usage of temporary table a hack. At worst, this trick can be considered as a more-complicated-than-necessary interface to the report. :-) And using such temporary table may actually be one of the good ways to improve performance. So, don't hurry writing it off. :-)