Re: Order by YYYY MM DD in reverse chrono order trouble

Thank you and Denis (denis@coralindia.com) - that was it.  I needed
explicit DESC for each ORDER BY criterium.

Otis

--- Stijn Vanroye <s.vanroye@farcourier.com> wrote:
> > Hello,
> > 
> > I am trying to select distinct dates and order them in the reverse
> > chronological order.  Although the column type is TIMESTAMP, in
> this
> > case I want only YYYY, MM, and DD back.
> > 
> > I am using the following query, but it's not returning dates back
> in
> > the reverse chronological order:
> > 
> > SELECT DISTINCT
> >   date_part('year', uu.add_date),  date_part('month', uu.add_date),
> 
> >   date_part('day', uu.add_date)
> > 
> > FROM uus INNER JOIN ui ON uus.user_id=ui.id INNER JOIN uu ON
> > ui.id=uu.user_id
> > WHERE uus.x_id=1
> > 
> > ORDER BY
> > date_part('year', uu.add_date), date_part('month', uu.add_date), 
> > date_part('day',  uu.add_date) DESC;
> > 
> > 
> > This is what the above query returns:
> > 
> >  date_part | date_part | date_part
> > -----------+-----------+-----------
> >       2004 |         2 |         6
> >       2004 |         4 |        20
> > (2 rows)
> > 
> > 
> > I am trying to get back something like this:
> > 2004 4 20
> > 2004 4 19
> > 2004 2 6
> > ...
> > 
> > My query is obviously wrong, but I can't see the mistake.  I was
> > wondering if anyone else can see it.  Just changing DESC to ASC,
> did
> > not work.
> > 
> > Thank you!
> > Otis
> What you could try to do in your order by clause is the following:
> ORDER BY
> date_part('year', uu.add_date) DESC,
> date_part('month', uu.add_date) DESC, 
> date_part('day',  uu.add_date) DESC;
> That way you are sure each of the fields is sorted DESC. if you don't
> specify a direction in your order by clause postgres will take ASC as
> the default. I think that he does "ASC,ASC,DESC" instead. I'm not
> sure if he applies the DESC to all specified fields in the order by
> if you declare it only once.
> 
> 
> Regards,
> 
> Stijn Vanroye
> 
> ---------------------------(end of
> broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if
> your
>       joining column's datatypes do not match