help on writing trigger

[sasi242]

Hi All
select * from products_brought;

pno pdate pqty sqty
1 02-sep-04 800
2 07-sep-04 250
3 09-sep-04 300

select * from products_sold;

sno sdate sqty
1 07-sep-04 300
2 10-sep-04 1000

the above mentioned are my tables where i am purchasing,selling records are enterd.

i would like to sell the last purchased products first(where sold date should be greater than purchase date) and i want to update the qtysold in the above purchase table.

Thanks In Advance

Sasidhar