Answer B is correct. An Integer data type of one form or another would be the correct choice for the type for the order number. The size of integer used would be determined based on the total number of orders maintained in the table over time. By the looks of the volume being discussed, it may even be worth considering an Alphanumeric data type. Small and Tiny integers would be out of the question because they don't provide for a size large enough to even hold a week's worth of data. Using an IDENTITY column is the simplest way to implement sequential numbering. It can be automated at the data store and thus guarantee uniqueness. The front-end application solution could easily produce duplicates between two different entry points. Using a UniqueIdentifier data type is never a good choice for any field value that has the possibility of being placed within a key or an index. The space taken up by this type of field will hamper performance of data inserts and retrievals. Although a TimeStamp data type would produce the necessary uniqueness, it would be cumbersome to work with as an order number.
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