I've written an entire book on this topic (Joe Celko's SQL programming style, ISBN 9780120887972). No, I am not going to post 200+ pages of text; you can get a copy from Amazon to take a look at it or check it out of the library.
It was largely based on the research that was done back in the 1970s, when software engineering was a magic buzzword. I was working for AIRMICS, an Army research group based at Georgia Tech. And we were contracting with various universities to do actual research on the readability of code.
Readability of text is measurable and not a matter of style or opinion. This is why my book includes "rationale" and "exceptions" subsections within each rule. Back then, we had to look at movies of people reading the screen or print out to manually track their eye movement. However, you could claim that all research is the study of graduate students and new employees who get to be guinea pigs 🙂
Another consideration applies to RDBMS is that the data element names will be used in places other than SQL. Some ISO standards are case-sensitive, and some are not. None of them allow embedded spaces. Some use different punctuation marks in their naming conventions. The Metadata Committee, ISO 11179, and other industry-standard groups have set up some conventions that are well worth following.
Please post DDL and follow ANSI/ISO standards when asking for help.