Обсуждение: Re: [SQL] 7.0 weirdness

gid is unique.. it's a serial..

funny thing is tho this worked on 6.5
oh well thanks for the info.


jeff

On Tue, 30 May 2000, omid omoomi wrote:

> Hi jeff,
> I'm not sure but may be that's because you are using select distinct and so 
> there would be a few rows with same "gid" but different "created" fields in 
> your table . And PG does not know which one to select and compare for ORDER 
> BY clause. If that ,you would need to change the table structure to a better 
> normal form.
> Regards ,
> Omid Omoomi
> 
> 
> >From: Jeff MacDonald <jeff@pgsql.com>
> >Reply-To: Jeff MacDonald <jeff@pgsql.com>
> >To: pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
> >Subject: [SQL] 7.0 weirdness
> >Date: Tue, 30 May 2000 09:28:11 -0300 (ADT)
> >
> >hi folks,
> >
> >this query works fine in 6.5 but screwie in 7.0
> >
> >7.0
> >
> >gm=> SELECT DISTINCT gid FROM members
> >gm-> WHERE active = 't'
> >gm-> AND  (gender = 0
> >gm->         AND  (wantrstypemale LIKE '%Short Term%'
> >gm->                 OR wantrstypemale like '%Marriage%'
> >gm->                 OR wantrstypemale like '%Long Term%'
> >gm->                 OR wantrstypemale like '%Penpal%'
> >gm->                 OR wantrstypemale like '%Activity Partner%')
> >gm-> )  order by created desc;
> >ERROR:  For SELECT DISTINCT, ORDER BY expressions must appear in target 
> >list
> >gm=>
> >
> >
> >any idea's ?
> >
> >jeff
> >
> >
> >
> 
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Hi,

Jeff MacDonald:
> gid is unique.. it's a serial..
> 
Then there is no point in using "DISTINCT" in the first place, is there?

> funny thing is tho this worked on 6.5

It happened to work because your gid is unique. But in the general case,
it can't work. Consider this table:

gid  createdX      1Y      2X      3

Now, should your query's result be

gidXY

or should it be

gidYX

? And since the typical implementation throws away non-selected-for
columns before UNIQUEing, how should it be able to sort anything?

-- 
Matthias Urlichs  |  noris network GmbH   |   smurf@noris.de  |  ICQ: 20193661
The quote was selected randomly. Really.       |        http://smurf.noris.de/
-- 
Problem mit cookie: File exists 

Jeff MacDonald <jeff@pgsql.com> writes:
> gid is unique.. it's a serial..

Mph.  If you assume that gid is unique then the query would give
well-defined results, but if you know it's unique then why don't
you just leave off the DISTINCT?

> funny thing is tho this worked on 6.5

No, 6.5 merely failed to notice that it was giving you undefined
results.
        regards, tom lane

Hi Jeff!

I think you need a solution, and not explains...
Tom, and the others told the truth. You missed this query.

> gid is unique.. it's a serial..
I give you two ways:

1) gid __realy__ unique  ->  DISTINCT is unnecessary.SELECT gid FROM members -- ... etc 

2) gid not unique  ->  DISTINCT is not enough. ;(SELECT gid,MAX(created) -- or MIN or AVG ... any aggregateFROM members
--... etcGROUP BY gid ORDER BY 2; -- second colunm
 

> > >gm=> SELECT DISTINCT gid FROM members
> > >gm-> WHERE active = 't'
> > >gm-> AND  (gender = 0
> > >gm->         AND  (wantrstypemale LIKE '%Short Term%'
> > >gm->                 OR wantrstypemale like '%Marriage%'
> > >gm->                 OR wantrstypemale like '%Long Term%'
> > >gm->                 OR wantrstypemale like '%Penpal%'
> > >gm->                 OR wantrstypemale like '%Activity Partner%')
> > >gm-> )  order by created desc;
> > >ERROR:  For SELECT DISTINCT, ORDER BY expressions must appear in target 

best regards
--nek;(

thanks for the hlep guys..

for those that are curious, the distinct is tehr cause it's
someone elses code that i'm workig on .. :) have to kick
out the bug's//

jeff

On Tue, 30 May 2000, Matthias Urlichs wrote:

> Hi,
> 
> Jeff MacDonald:
> > gid is unique.. it's a serial..
> > 
> Then there is no point in using "DISTINCT" in the first place, is there?
> 
> > funny thing is tho this worked on 6.5
> 
> It happened to work because your gid is unique. But in the general case,
> it can't work. Consider this table:
> 
> gid  created
>  X      1
>  Y      2
>  X      3
> 
> Now, should your query's result be
> 
> gid
>  X
>  Y
> 
> or should it be
> 
> gid
>  Y
>  X
> 
> ? And since the typical implementation throws away non-selected-for
> columns before UNIQUEing, how should it be able to sort anything?
> 
> -- 
> Matthias Urlichs  |  noris network GmbH   |   smurf@noris.de  |  ICQ: 20193661
> The quote was selected randomly. Really.       |        http://smurf.noris.de/
> -- 
> Problem mit cookie: File exists 
>