I'm building a patching system in our environment. In discussion with my team, we were talking about how a CU could be "skipped" and that by adding a later CU you would get the earlier CU. That made sense, until we started thinking through all the circumstances, for instance SQL Server 2012 SP1 CU1 can't be applied on an instance that's on SQL Server 2012 RTM, CU7. Why? You'd be skipping SP1. You would first have to patch the machine from the RTM to SP1, and then apply SP1's CU1.
Assuming what I said is correct, does anyone know if SQL will ALWAYS prevent a QFE/PATCH/SP from being applied out of order?
The reason I'm asking is that we are going to create a database table of patches that are completed on instances, and if something is "skipped" but in reality completed (like going from SP1 CU1 to SP1 CU 5), I need to make hard and fast rules so that I can have a process enter the data in the tables.