I’d give recommendations, but I haven’t read any books on programming since college (too many decades ago). I only read the manuals and sources such as the Information Centers, plus some results from directed web searches.
Do you have particular areas you want to learn? Maybe some sources exist that are well suited.
I may not know enough to answer that question. Embedded SQLRPGLE for joining data, pullnig data, sorting data, later; updating.
How much do you know about SQL to start with? Generally, the topics you mentioned might be better covered from a pure SQL viewpoint first. Then would come details of translating into a HLL language.
IMO, if embedded SQL is where you want to do reading, I’d say to read the IBM topics on it before anything else. It’s not as important to understand it when you read it — it’s more important that you only get the words in mind to have memories of having seen it before when you run into obstacles.
I’d say that you should finish the Coding SQL statements in ILE RPG applications while looking for other sources. You might then look at Info Center topics that surround that one to see what catches your interest.
A huge amount of info can be gained by reading without understanding. The mind continues to go over it unconsciously. If you’ve put it into your head, everything you read later will be much easier to grasp.