How do people keep track on all the features that are added in RDMS? When you know the basic stuff like SELECT / JOIN / indexes ect ... how do you stay relevent with new things added?
So I guess it's tech like any other. The more you know and use, the more you're aware of the recent developments. Like pretend you know enough javascript to build small promotional websites with some animations as you scroll down the page. You probably don't care, and are not aware, of the recent developments around optional chaining operators.
1. Through blog posts like this
2. Needing something in the moment and googling.
To elaborate on #2, I learned about partial indices when I was at a situation at work when I needed to optimize indices for a heavily used table. Google eventually brought me to their excellent docs and SO posts that mentioned them.
https://www.postgresql.org/about/featurematrix/
This is not an exhaustive list, but it contains a lot. You would still have to cull information from release notes:
https://www.postgresql.org/docs/release/
Or looking at the documentation page for a command (e.g. SELECT), or as per other suggestions, reading blogs/articles.
By reading the release notes
then read the chapters you didn't understand the title or haven't heard about the concept. this might take a while if you only know about select and join and create index - abstractions SQL provides are more leaky than rusty buckets and the manual is there to tell you everything about these and how to work with them.
then it's 'just' a matter of keeping up with the delta by reading release notes.