Hi Richard,
Could you please explain a little bit more why we shouldn't eliminate the LeadSource and Shipping fields from the MANY CustomerT (in the One-to-Many Relationship of LeadSourceT to CustomerT), but we are eliminating the FirstName to Phone number fields in the MANY ContactT (in the One-to-Many Relationship of CustomerT to ContactT)? Shouldn't we also eliminate those fields in the CustomerT, since they are redundant data? (whether they are good data or not?) Thanks!

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Reply from Richard Rost:

It's been a while since I recorded this, but if memory serves, LeadSourceT was just a helper table that contains a list of possible lead sources. You would store that once in the customer table.

Generally, you want to prevent duplicate data in your database, however there are some exceptions as I will cover in later classes. For example, you generally want to store the customer's address only ONCE in the customer table, HOWEVER, there is the exception where you might want to store the address on EACH order he places, so you know where THAT order was shipped. Historical data is one of the exceptions, and I cover more in future lessons (for example, performance increases, etc.)