Re: PostgreSQL 10 changes in exclusion constraints - did something change? CASE WHEN behavior oddity

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-06-08 23:05:53 -0400, Tom Lane wrote:
>> ... The first
>> attached patch does it that way, and it seems nice and clean, but I ran
>> into a complete dead end while trying to extend it to handle related cases
>> such as disallowing SRF-inside-aggregate or nested SRFs in FROM.

> But, do we really need to handle those? IOW, isn't handling
> CASE/COALESCE, which we can recognize early in parse analysis,
> sufficient to error out here? It'd be a lot nicer if we could error
> about SRF arguments to aggregates et al. during analysis rather than
> execution, but there's not a comparably huge need to improve there.

Yes, we already have guards for those cases, but they return fairly opaque
error messages to the tune of "set-valued function called in context that
cannot accept a set", because the executor hasn't enough context to do
better. I'd like the messages to be more specific, like "set-valued
function cannot appear within CASE" and so on. Anyway the point here is
to evaluate different approaches to changing the parser on the basis of
whether they *could* be extended to handle related cases. Whether we
actually do that right now is less important.

regards, tom lane