Re: get only rows for latest version of contents - Mailing list pgsql-sql

Hi Erik

Thx for your suggestion.
I've done some tests and correct the order to get what i want.

In fact the order i would like to have is 3,2,1,null (null is a draft
version on my api).
But the order ASC gives 1,2,3,null
And the order DESC gives null,3,2,1
So i use order by -(version_no) that gives me 3,2,1,null

SELECT DISTINCT ON (Idnode) Idnode, version_no, c1, c2, c3
FROM business
GROUP BY Idnode, version_no, c1, c2, c3
ORDER BY Idnode, -(version_no) DESC;

But finally, when i have wanted to inject this way in my real big request it
gives me error:
SELECT DISTINCT ON expressions must match initial ORDER BY expressions
Because my api requires a different order and it seems idnode should be in
first of the order to be able to use DISTINCT ON.

So for now, i'll keep Chris solution.
I have not profile it with large tables but it's the only solution i have
for now ;)

Thx everybody.
Regards
Sebastien


> -----Message d'origine-----
> De : Erik Jones [mailto:erik@myemma.com]
> Envoyé : jeudi 25 octobre 2007 16:35
> À : Sébastien Meudec
> Cc : 'Christian Kindler'; pgsql-sql@postgresql.org
> Objet : Re: [SQL] get only rows for latest version of contents
>
>
> On Oct 25, 2007, at 1:50 AM, Sébastien Meudec wrote:
>
> > Thx a lot Chris.
> >
> > In fact the correct SQL was (rewritten with inner join because of
> > it is
> > required by my api):
> >
> > select b1.*
> > from business b1
> > inner join (select idnode,max(version_no) as version_no from business
> >             group by idnode) as b2
> > on b1.idnode = b2.idnode and
> >   (b1.version_no = b2.version_no or b2.version_no is null)
> >
> > Regards,
> > Seb.
> >
> >
> >> -----Message d'origine-----
> >> De : pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-
> >> owner@postgresql.org] De la part de Christian Kindler
> >> Envoyé : mercredi 24 octobre 2007 11:55
> >> À : Sébastien Meudec
> >> Cc : pgsql-sql@postgresql.org
> >> Objet : Re: [SQL] get only rows for latest version of contents
> >>
> >> Hi!
> >>
> >> not quick mut works
> >>
> >> select * from business b1
> >> where b1.version_no = (SELECT max(version_no) FROM business b2.
> >>                         where b2.idnode = b1.idnode
> >>                        )
> >>
> >> If you want to make this quiry faster du a regular join
> >>
> >> select b1.*
> >>   from business b1,
> >>        (SELECT max(version_no) FROM business b2.
> >>          where b2.idnode = b1.idnode
> >>        ) as b2
> >> where b1.idnode = b2.idnode
> >>   and b1.version_no = b2.version_nr
> >>
> >> Regards Chris
> >>
> >> PS written without running any sql, maybe there are some syntax
> >> issues,
> >> but i am shure you will figure these out :-)
> >>
> >>
> >>
> >> On Wed, October 24, 2007 11:29 am, Sébastien Meudec wrote:
> >>> Hi everybody.
> >>>
> >>> I have a table like that (i simplified it):
> >>> CREATE TABLE business {
> >>>   idnode integer not null,
> >>>   version_no integer,
> >>>   c1 text,
> >>>   c2 text,
> >>>   c3 text
> >>> }
> >>> With a unique index in (idnode,version_no).
> >>>
> >>> This table records many version from contents identified by
> >>> idnode where
> >>> texts may be different.
> >>> So i can have:
> >>> Idnode | version_no | c1    | c2    | c3
> >>> 111    | 2          | foo1  | foo2  | foo3
> >>> 111    | 1          | fee1  | foo2  | foo3
> >>> 111    | null       | fee1  | fee2  | fee3
> >>> 222    | null       | too1  | too2  | too3
> >>> 333    | 1          | xoo1  | xoo2  | xoo3
> >>> 333    | null       | yoo1  | yoo2  | yee3
> >>>
> >>> I want to select all columns but only for last (greatest) version of
> >> each
> >>> content. So I want a result like:
> >>> Idnode | version_no | c1    | c2    | c3
> >>> 111    | 2          | foo1  | foo2  | foo3
> >>> 222    | null       | too1  | too2  | too3
> >>> 333    | 1          | xoo1  | xoo2  | xoo3
> >>>
> >>> If i do:
> >>> SELECT idnode, max(version_no) FROM business
> >>> GROUP BY idnode ORDER BY idnode;
> >>>
> >>> I get effectively only last version:
> >>> Idnode | version_no
> >>> 111    | 2
> >>> 222    | null
> >>> 333    | 1
> >>>
> >>> But as soon that i want to get texts, I don't know how to build
> >>> the SQL.
> >>> In each SQL i tested i've been forced to put text column in a
> >>> group by
> >>> since
> >>> i used aggregate for version_no:
> >>> SELECT idnode, max(version_no), c1, c2, c3 FROM BUSINESS
> >>> GROUP BY idnode, c1, c2, c3 ORDER BY idnode;
> >>>
> >>> But with that SQL, because of the group by and different values
> >>> in text
> >> i
> >>> get
> >>> Idnode | version_no | c1    | c2    | c3
> >>> 111    | 2          | foo1  | foo2  | foo3
> >>> 111    | 1          | fee1  | foo2  | foo3
> >>> 111    | null       | fee1  | fee2  | fee3
> >>> 222    | null       | too1  | too2  | too3
> >>> 333    | 1          | xoo1  | xoo2  | xoo3
> >>> 333    | null       | yoo1  | yoo2  | yee3
> >>>
> >>> As we can't do aggregate in join neither in where, i can't get
> >>> what i
> >>> want.
> >>>
> >>> Anybody could help me to build proper SQL ?
> >>>
> >>> Thx for your answers.
> >>> Sébastien.
>
> Here's another little trick that can come in handy for this:
>
> SELECT DISTINCT ON (Idnode) Idnode, version_no, c1, c2, c3
> FROM business
> ORDER BY Idnode, version_no DESC;
>
> Erik Jones
>
> Software Developer | Emma®
> erik@myemma.com
> 800.595.4401 or 615.292.5888
> 615.292.0777 (fax)
>
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