Re: Syntax bug? Group by? - Mailing list pgsql-hackers

Andrew Dunstan <andrew@dunslane.net> writes:
> Mark Woodward wrote:
>> My question, is it a syntactic technicality that PostgreSQL asks for a
>> "group by," or a bug in the parser?

> AFAIK what you want is not per sql spec.

It would in fact be a violation of spec.  Consider the case where there
are no rows matching 15.  In this case

select min(tindex), avg(tindex) from y where ycis_id = 15;

will yield one row containing NULLs, whereas

select min(tindex), avg(tindex) from y where ycis_id = 15 group by ycis_id;

will yield no rows (because there are no groups).  Therefore, if
Postgres were to implicitly insert a GROUP BY to make it legal to
reference ycis_id directly, we'd be changing the query behavior
and breaking spec.
        regards, tom lane