Hi,all!

I want to write a HQL like this SQL:
SELECT begin.subject, sum(begin.debit) AS bgdebit, sum(end.debit) AS enddebit
FROM VoucherItem begin
LEFT JOIN VoucherItem end ON begin.subject = end.subject
WHERE begin.year='2009' AND begin.month<'05' AND end.year='2009' AND end.month='05'
GROUP BY begin.subject

But,I don't know how to write this in HQL.

No 'on' , No relationship.How to write it???
Thanks :)