NoSQL databases are just a tool like other tools. And you should know when and why to apply such tools not just dismiss learning them altogether.
Also every developer goes on their own journey. So if someone wants to build a social network then a graph database is going to make more sense even at the beginning than a relational one.
As for NoSQL. I'd say that definitely should be on the roadmap. I've assumed that they've already learned RDBMS, but knowing when to use the two is essential. Most companies now are working with data lakes and unstructured data (e.g. user and session data). Knowing how to get around that flexibility, how to structure your business logic and models, and what tool to pick (i.e. Redis for caching), etc. goes alongside NoSQL knowledge.
I had a bad experience with a project that I was assigned to "help". The build steps documented used incompatible lib version. It's hard to help if you can't even build/run their codes.
Postgres even supports using NoSQL concepts with JSONB so there’s no reason not to start with it.
I’m sure I’ll get downvoted since HN has been very hostile to real talk lately but I don’t care.
Also distinguishing NoSQL and SQL is quite old and still dating from the CAP theorem which is also becoming obsolete. You have traditional databases and the rest since 'NoSQL' are incorporating SQL features (ACID, joins, etc) and vice-versa, soon it will just be databases with feature X,Y,Z. If you want to add something I would rather add 'distributed databases'. Learn relational databases probably boils down to 'learn SQL'
Knowing which database to use in the landscape is extremely important.
It should imo be: - Learn SQL - Learn GraphQL (becoming the new SQL quickly) - Learn gRPC - Learn about database features (consistency, distribution, replication, sharding, OLTP, OLAP) and what database to use in which situation.
"Learn GraphQL" - I'm not sure you need to learn GraphQL. You need to now that GraphQL is a powerful tool for APIs consumed by third party devs, such as the GitHub or Facebook API. But for internal APIs (and more than 98% of APIs are internal!), GraphQL (and even REST) is overkill and you'd be better off with RPC, such as Wildcard API [1] or gRPC [2]. Many developers will never have to build a GraphQL API in they entire career. Only few companies need to expose their data to third parties.
[1]: https://github.com/reframejs/wildcard-api
[2]: https://grpc.io/