How to find missing data from one table that is a join of two other tables

I have two tables, stock and location, with a third table that retains the level of stock at each location, stock_loc_info. Each stock item should have a row for each location. What SQL query would show that the row B1 is missing from stock_loc_info? stock.stockcode --------------- A B location.locno -------------- 1 2 stock_loc_info.fkstockcode stock_loc_info.fklocno -------------------------- ---------------------- A 1 A 2 B 2