Upgrade SQL Server, not user databases I have one machine we've been fighting to do an in place upgrade of SQL Server from 2016 SP2 CU3 to 2017. It keeps failing, but that's another topic. My question is, is there a way I can run the upgrade, but force it to omit upgrading user databases to 2017?

If I can get the system databases upgraded and the server running I'll manually upgrade user databases at another time.
No. As soon as you attach a database to SQL Server, assuming it is compatible, the internal system tables will be upgraded.

While this process is a one-way operation, it takes a few seconds at most.

If you do not wish to upgrade your user databases, don't upgrade to the latest SQL Server.

If you want to keep your databases on a previous compatibility level, that can be done from T-SQL code or inside SQL Server Management Studio, but for all intents and purposes, the internal version of the database will match that of the instance it is installed on.