SQL - joining files and counting records with file that has "one-to-maybe" relationship

SQL - joining files and counting records with file that has "one-to-maybe"
relationship

I have 3 files
Order Header- has order#
Order Detail - details lines with product code and qty , keyed on order#
Consigned Item file - list of consigned products (think products that we
sell but are owned by someone else). not all products we sell are
consigned; this file contains a subset of product master file.
and I want to produce this resultset:
Order Number Order Date Number of lines Total Qty Total
Consigned Qty
1 20130101 5 10 5
2 20130101 4 20 0
3 20130101 7 41 20
4 20130101 1 66 66
my query looks like this (simplified)
SELECT H.OrderNo, H.Date, Count(D.LineNo), Sum(D.ProdQty)
FROM Header H
JOIN Detail D ON (H.PO# = D.PO#)
WHERE H.DATE > 20130101
GROUP BY H.PO#, H.Date
ORDER BY H.PO#, H.Date
Consigned Qty in the report represents the number of matches from product
code on the detail file to product code on the consignment file multiplied
by the quantity on the detail line.
My problem is getting consigned qty because I have a "one to maybe"
relationship between "Detail File" and "Consignment File". Do I need a
temporary table here, sub-select, some hand coding on each fetch?
I am using IBM/DB2 SQL, so no mysql/mssql/oracle specific tricks please.
thanks