In the 1990s C.J.Date said: "The rule by which it is determined within the standard that one key word needs to be reserved while another need not be is not clear to this writer."
Nothing has changed since then, except there are more reserved words. No DBMS uses the standard list. So I think that it is probably best to know what words are reserved in product X that are not reserved in product Y. If you know, you can avoid syntax errors when you update or migrate.
I'll present several comparisons, ending with a grand chart of all the reserved words in the standard and six current DBMSs.
First here's a screenshot of ocelotgui where I'm hovering over
the word BEGIN.
What I'm illustrating is that you can't depend on intuition and assume BEGIN is reserved, but a GUI client can tell you from context: it's a …