OK, I see what's going on. I can have more than one max(amount) with
the same amount and payee. Thanks so much. Like I said, it's sort of
dogged me off and on many times.
Thanks.
Bill Moran wrote:
Omar Eljumaily <omar2@xxxxxxxxxxxx> wrote:
Sorry if this isn't exactly postgresql specific. I periodically run
into this problem, and I'm running into it now. I'm wondering if
there's something about "group by" that I don't understand. As an
example what I'd want to do is return the "id" value for the check to
each payee that has the highest amount. It seems like there's no
problem with ambiguity in logic, but postgresql + other sql servers balk
at it. The group by fields need to explicitly match the select fields
with the exception of the aggregate function(s?).
create table checks
{
id serial,
payee text,
amount double
};
select max(amount), payee, id from checks group by payee;
Why won't the above work? Is there another way to get the id for the
record with the highest amount for each payee?
Because it's ambiguous. If you're grabbing max() for amount, which
id tuple do you want?
Perhaps the way you're storing your data, those answers aren't ambiguous,
but the database doesn't know that. Take this query as an example:
select max(amount), max(checknumber), payee from checks group by payee;
In that case, the highest checknumber and the highest check amount
probably won't come from the same tuple. If you were to throw in
there:
select max(amount), max(checknumber), payee, id from checks group by payee;
Which id does it give you? The one that matches max(amount) or the one
that matches max(checknumber)?
