No Can you please explain it in details ? Actually in my case I have to fetch the data from existing database (NAV) and I can not amend the structure of that database.
I'm sorry, I misunderstood your question. In my answer, I was saying that I have added a new column to Nop's Products table called "ExternalId", which is a reference to a product ID on another system that our nop-based website will have to integrate with.
For your case, it may be tricky. If you look inside Nop.Data/Mappings, you can see how each property of nop's domain objects (category/manufacturer/product/order etc etc) are "mapped" to their respective database tables & columns. Perhaps you could change these to match to your database structure?
Although unfortunately I suspect that this would take a lot of work.