[TriLUG] OT: SQL "Group by" question

[Thomas]

This works in Oracle, but I'm not sure about postgressql,

select assign_id, isbn, assign_date
from assign
where (isbn, assign_date) in
(select isbn, max(assign_date)
from assign
group by isbn);



On 10/3/06, Andrew Perrin <clists at perrin.socsci.unc.edu> wrote:
>
> Yes, I understand it in that direction. It's the other direction I'm
> concerned about - I would like not just the date and isbn, but also the
> assign_id of the record returned by the max(assign_date) aggregate.
>
> Thanks,
> A
>
> ----------------------------------------------------------------------
> Andrew J Perrin - andrew_perrin (at) unc.edu -
> http://perrin.socsci.unc.edu
> Assistant Professor of Sociology; Book Review Editor, _Social Forces_
> University of North Carolina - CB#3210, Chapel Hill, NC 27599-3210 USA
> New Book: http://www.press.uchicago.edu/cgi-bin/hfs.cgi/00/178592.ctl
>
>
>
> On Tue, 3 Oct 2006, Cristobal Palmer wrote:
>
> > You /have/ to have the column you want to group by in the select
> > statement. How can you group by values in a column that you didn't
> > retrieve? You have to have those values.
> >
> > The prof in my database class beat us over the head with this one. If
> > you want a more detailed answer I can dig up the class notes on that.
> >
> > -CMP
> >
> > On 10/3/06, Andrew Perrin <clists at perrin.socsci.unc.edu> wrote:
> >> Sorry for the slightly OT post, but my soft-science mind is having
> trouble
> >> wrapping itself around an SQL problem.
> >>
> >> I have a table of book-review assignments, including a unique
> identifier
> >> (assign_id); the book's isbn (isbn); and the date we made the
> assignment
> >> (assign_date). There are often numerous assignments per isbn. I would
> like
> >> to retrieve the assign_id of the *latest* assignment per isbn.  I can
> get
> >> this far:
> >>
> >> select assign.isbn, max(assign.assign_date) as last_assign_date from
> >> assign group by assign.isbn;
> >>
> >> ...which will give me the isbn and latest assign date, but of course I
> >> can't just ask for the assign_id in the way that seems obvious to me:
> >>
> >> select assign.assign_date, assign.isbn, max(assign.assign_date) as
> >> last_assign_date from assign group by assign.isbn;
> >>
> >> because assign_date isn't in the GROUP BY clause.
> >>
> >> I can't imagine there isn't an accepted answer to this - any advice? I
> am,
> >> by the way, using postgresql 8.1 on debian linux.
> >>
> >> Thanks,
> >> Andy
> >>
> >> ----------------------------------------------------------------------
> >> Andrew J Perrin - andrew_perrin (at) unc.edu -
> http://perrin.socsci.unc.edu
> >> Assistant Professor of Sociology; Book Review Editor, _Social Forces_
> >> University of North Carolina - CB#3210, Chapel Hill, NC 27599-3210 USA
> >> New Book: http://www.press.uchicago.edu/cgi-bin/hfs.cgi/00/178592.ctl
> >>
> >>
> >> --
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> >>
> >
> >
> > --
> > Cristobal M. Palmer
> > UNC-CH SILS Student -- ils.unc.edu/~cmpalmer
> > TriLUG Vice Chair
> > "There are many roads to enlightenment, and thus many roads back to
> > the One True Debian" --crimsun
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