Re: handling of COUNT(record) vs IS NULL

Sam Mason <sam@samason.me.uk> writes:
> I've just noticed that the handling of COUNT(record) and (record IS
> NULL) aren't consistent with my understanding of them.  If I run the
> following query:

>   SELECT
>      NULL       IS NULL, COUNT( NULL      ),
>     (NULL,NULL) IS NULL, COUNT((NULL,NULL));

> The IS NULL checks both return TRUE as I'd expect them to, but the
> second count doesn't return 0.

THe fourth of those isn't really valid SQL.  According to SQL99,
IS NULL takes a <row value expression> as argument, so it's valid
to do (NULL,NULL) IS NULL, but COUNT takes a <value expression>.

I don't see anything in the spec suggesting that we are supposed
to drill down into a rowtype value to see whether all its fields
are null, in any context other than the IS [NOT] NULL predicate.

            regards, tom lane