Re: [HACKERS] No: implied sort with group by

> > Not necessarily true; as I said, I get the same result as above (with the 980112
> > source tree; have things changed since??). Perhaps you are running into the sorting
> > problem which seemed to be present on larger tables only?
> >
> > postgres=> select b,c,sum(a) from t1 group by b,c;
> > b|c|sum
> > -+-+---
> >  |x|  5
> >  |z|  3
> > (2 rows)
> >
> > postgres=> select * from t1;
> > a|b|c
> > -+-+-
> > 1| |x
> > 2| |x
> > 2| |x
> > 3| |z
> > (4 rows)
>
> Hmmm...I have a snapshot from about ten days ago

> Is the order from the second query the order that the rows were inserted?
>
> Do you get the same results if you insert the (3,null,'z') second or third so
> the rows are stored out of order?  I was getting my bad results with this same
> data, only four rows.

OUCH! You are right, there is a problem with this simple test case:

postgres=> select b,c,sum(a) from t1 group by b,c;
b|c|sum
-+-+---
 |x|  5
 |z|  3
 |x|  0
(3 rows)

postgres=> select * from t1;
a|b|c
-+-+-
1| |x
2| |x
2| |x
3| |z
0| |x
(5 rows)

I just inserted a single out-of-order row at the end of the table which, since the
integer value is zero, should have not affected the result. Sorry I didn't understand
the nature of the test case.

                                                    - Tom