Andrew Dunstan <[EMAIL PROTECTED]> 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
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
