Is querying on views slower than doing one query?

Question

Will Mssql be even fast when I query on a view opposed to one query?

example

When I have this view:

create view ViewInvoicesWithCustomersNam         


        

Answer 1

A view is simply a macro that is expanded/unnested into the main query. So these are equivalent.

Note: if customername is in the Customer table, you've actually created an INNER JOIN. To filter for Bart's invoices and invoices with no customer you'd need to do this:

select
  *
from
  Invoices
  left join
  Customer on Customer.ID=Invoices.CustomerID and customername="Bart"