"David G. Johnston" <david.g.johnston@gmail.com> writes:
> Fair, we don’t explicitly document that ‘…’ || NULL yields NULL. It’s more
> of “unless otherwise noted doing stuff with null results in unknown/null
> outcomes”.
Yeah, there's a documentation gap here. I dug around a little and
really couldn't find anything anywhere in our SGML docs that explains
NULL in any detail; we tend to assume that you've already heard of it.
There are a couple of parenthetical remarks in func.sgml that
reference the notion that NULL means "unknown", but you'd never
find those if you were looking for an explanation of what NULL is.
Perhaps that'd be worth a few paras somewhere, though I'm not
very sure where's a good place.
regards, tom lane