MySQL aside, your first query will end up an error if Customer.Name is not functionally dependent on Customer.B. This highlights that there could be different c

MySQL aside, your first query will end up an error if Customer.Name is not functionally dependent on Customer.B. This highlights that there could be different customers with the same name and that it was a poor query to start. For number 2, that's exactly what inner join means otherwise use a left join. The first question someone should ask themselves is if they want all customers or only ones that have had sales.