Re: Allow subfield references without parentheses

Peter Eisentraut <peter(at)eisentraut(dot)org> writes:
> This patch allows subfield references in column references without
> parentheses, subject to certain condition. This implements (hopes to,
> anyway) the rules from the SQL standard (since SQL99).
> This has been requested a number of times over the years. [0] is a
> recent discussion that has mentioned it.

The obvious concern about this is introduction of ambiguity where
there was none before.

> If both possible interpretations apply, then an error is raised. (A
> workaround is to change the alias used in the query.) Such errors
> should be very rare in practice.

Not sure if it's rare or not, but I agree with raising an error rather
than silently choosing one alternative. We won't find out if it's
problematic unless we throw an error.

> ... I also studied ruleutils.c a
> bit to see if there are any tweaks needed to support this. So far it
> seems okay. I'm sure we can come up with some pathological cases, but
> so far I haven't done anything about it.

I assume that what will happen is that ruleutils will continue to emit
our traditional notation with the extra parentheses. I think we need
to leave it like that, so as not to create a compatibility booby-trap
for loading dumps into older PG versions.

regards, tom lane