Re: Old question - failed to find conversion function from "unknown"

>Well, it would obviously be better if PG could figure out it was safe,
>but I'm not sure there's a general case where it is. You can see it's OK
>because you know there's only one row in your SELECT result-set.

I think, it's OK because NULL can be compared with anything
with predictable result and no additional information about
types is necessary.
Is it correct vision?

I agree it's hard to proceed your query with UNION
and some sort of error is reasonable here.

--
Best regards
Ilja Golshtein