I am a bit lost in a little SQL problem, to which I need an answer. It will probably be a triviality to you guys. Nevertheless, I am designing a database (it's a uni exercise) and there is a requirement to keep historical data of prices for products. Thus I have a table PRODUCT and table PRODUCTPRICE. Product has a primary key ProdCode. And PRODUCTPRICE has a primary key ProdCode (it's a foreign key as well) and a StartDate. The combination of ProdCode and StartDate would create a PK. An price record with NULL in the EndDate would be the current price of the product. Please let me know if this make sense to you. Ask any subsequent questions if you need more info please. Thank you a lot guys. I am also uploading a diagram of the exercise, if you could please let me know if it makes sense to you. Please remember this is only a database analysis exercise not a real system.