I'm not familiar with PROGRESS. Do you have a DBA or developer you can talk with about how to write this SQL?
As an example, assuming a PO_DETAIL table with the following structure:
Cust_Number
PO_Number
Part_Number
PO_Date
Unit_Price
The SQL would look something like this (trying to use ANSI Standard SQL - You may have to change it to fit your database):
Select PO_DETAIL.PO_Number, PO_DETAIL.Part_Number,
PO_DETAIL.PO_Date, PO_DETAIL.Unit_Price,
PREV_PO_DETAIL.Unit_Price as Prev_Price
from PO_DETAIL
left outer join PO_DETAIL as PREV_PO_DETAIL on
PREV_PO_DETAIL.Cust_Number = PO_DETAIL.Cust_Number
and PREV_PO_DETAIL.Part_Number = PO_DETAIL.Part_Number
and PREV_PO_DETAIL.PO_Date < PO_DETAIL.PO_Date
where PREV_PO_DETAIL.PO_Date is null
or PREV_PO_DETAIL.PO_Date =
(Select Max(CHK_PO_DETAIL.PO_Date)
from PO_DETAIL as CHK_PO_DETAIL
where CHK_PO_DETAIL.Cust_Number = PO_DETAIL.Cust_Number
and CHK_PO_DETAIL.Part_Number = PO_DETAIL.Part_Number
and CHK_PO_DETAIL.PO_DATE < PO_DETAIL_DATE)
-Dell
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