Both Standard and Enterprise editions of SQL Server come with a lot more than just a database engine, there’s also a suite of BI tools:
- Integration Services (SSIS)
- Reporting Services (SSRS)
- Analysis Services (SSAS)
which you are also licensed to use on the same server as the database engine. That might be OK for a small business, however many of the BI projects I have worked on have needed individual servers for some of these components, and then things get more complicated.
Essentially if you put a server component of SQL Server (as distinct from the client tools which I’ll come back to) then you must license that server as well. e.g. you might have Server A with the database engine on and all your databases, while Server B might have Reporting and Analysis Services on and both of these must have an appropriate license of SQL Server.
Which edition is up to you, so your server running database engine might be Enterprise edition, while you might only need Standard edition for your reporting services server.
When it comes to the licensing model you want again each server can be different so Integration Services might only need a 5 CAL license because it isn’t accessed by anyone, but reporting services is opened up to the internet and so must have CPU licensing.
Finally the client tools are not licensed themselves and this includes the client connectivity tools, BI Development Studio, SQL Server Management Studio and the Report Builder, so you can deploy those as needed.
For more information on this complex topic: