Licensing is really complex, but as long as you know these seven rules, you can go a long way:
- If you query it, you have to license it.
- “It” means the Windows environment – all of the processor cores that Windows sees. (Things get a little weirder under virtualization.)
- Offloading a backup or a DBCC is considered querying until you license 2019 with Software Assurance.
- If you license it, and you pay Software Assurance, you get exactly one or more standby servers of equivalent size. (Standby means you’re not querying it.) Details here.
- Standard Edition costs about $2k USD per core, but caps out at 16 cores and 128GB RAM (for SQL 2014, or 64GB for 2012).
- Enterprise Edition costs about $7k USD per core.
- Software Assurance is an additional annual fee that gives you free upgrades as long as you keep paying for it.
Then to learn more, check out Microsoft’s SQL Server licensing resources.