how to retrieve values from 3 table

i have 3 table namely called sales2, and purchase2, and purchase_return . the sales2 table contain the following fields

selling prodname,prodcode,billamount,barcode, sales qty. 

purchase_return table contains following fields

prodname,prodcode,barcode,return_qty

purchase2 table contains

purchase value for single qty, and purchased qty and invoice date, entry date

Now I want to retrieve all the detail group by prodcode but if sales2 contains prod qty then it suptract from purchase2 if purchase_return contains qty field then it also subtract from purchase2 table how to display as my need