Importing data

When importing data, if a product has the same product code will it update the item or will it create a duplicate item?

If I export all of my products, modify the csv and then to import, should I check the box that says delete exisiting products or will cs cart know to update the existing products?

Cs Cart will update existing products if the same code is used.

if by accident you have 2 codes the same, when the second one gets imported it will overwrite the firts with the same info

Dont delete existing data if you dont need too