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Re: help on SQL

From: Michael Stephenson <mstephenson(at)tirin(dot)openworld(dot)co(dot)uk>
To: Gergely Czuczy <phoemix(at)harmless(dot)hu>
Cc: Kenneth Suralta <ksuralta(at)ntsp(dot)nec(dot)co(dot)jp>,pgsql-interfaces(at)postgresql(dot)org
Subject: Re: help on SQL
Date: 2004-04-21 10:38:25
Message-ID: Pine.LNX.4.58.0404211033560.31842@tirin.openworld.co.uk (view raw or flat)
Thread:
Lists: pgsql-interfaces
In postgres (or in SQL in general) there isn't a natural way of expressing
what you want to do.

I suppose you could do something like:

create temp sequence dataseq;
select data from data where nextval('dataseq') % 3 = 1;
drop sequence dataseq;

Which'll do the job, but is a bit nasty.

Michael

Web Applications Developer
Open World Ltd, 11 Riverside Court, Riverside Road, Bath, BA2 3DZ.
Tel: +44 1225 444950  Fax: +44 1225 336738  http://www.openworld.co.uk/

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On Wed, 21 Apr 2004, Gergely Czuczy wrote:

> hello
>
> what you have done is not the thing that was asked. you've retrieved every
> row that has a spacial value(data-1 %3). the request was to retrieve every
> 3rd row. the difference is that, the 'every Nth' row has nothing to do
> with the value of any field in the row. try to retrieve every Nth row from
> a query where there are no integer values, only timestamps and string. or
> try to do your method where the integer value is not continous.
>
> On Wed, 21 Apr 2004, Michael Stephenson wrote:
>
> > test=# create table data (data int);
> > CREATE
> > test=# insert into data values(1);
> > INSERT 3531768 1
> > test=# insert into data values(2);
> > INSERT 3531769 1
> > test=# insert into data values(3);
> > INSERT 3531770 1
> > test=# insert into data values(4);
> > INSERT 3531771 1
> > test=# insert into data values(5);
> > INSERT 3531772 1
> > test=# insert into data values(6);
> > INSERT 3531773 1
> > test=# insert into data values(7);
> > INSERT 3531774 1
> > test=# select * from data where (data - 1) % 3 = 0;
> >  data
> > ------
> >     1
> >     4
> >     7
> > (3 rows)
> >
> > test=#
> >
> > HTH
> >
> > Michael
> >
> > Web Applications Developer
> > Open World Ltd, 11 Riverside Court, Riverside Road, Bath, BA2 3DZ.
> > Tel: +44 1225 444950  Fax: +44 1225 336738  http://www.openworld.co.uk/
> >
> > CONFIDENTIALITY NOTICE
> > The information contained in this message is confidential, intended only for
> > the use of the individual or the entity named as recipient. If the reader of
> > this message is not that recipient, you are notified that any
> > dissemination,
> > distribution or copy of this message is strictly prohibited. If you have
> > received this message in error, please immediately notify us by telephone on
> > the number above. Your co-operation is appreciated.
> >
> > On Wed, 21 Apr 2004, Kenneth Suralta wrote:
> >
> > > hi gergely,
> > >
> > > thanks for replying..
> > > what i mean is supposing there is a table with the following rows:
> > >
> > >  data
> > > -----
> > > 1
> > > 2
> > > 3
> > > 4
> > > 5
> > > 6
> > > 7
> > >
> > > is it possible to get every other N-row in the table?
> > > example, if N is 3.
> > > data
> > > -----
> > > 1
> > > 4
> > > 7
> > >
> > > thanks,
> > > kenneth
> > >
> > >
> > >
> > > Gergely Czuczy wrote:
> > >
> > >  On Wed, 21 Apr 2004, Kenneth Suralta wrote:
> > >
> > >
> > >
> > >  hello everyone,
> > >
> > > is it possible to get every other row in the table?
> > > like for example:
> > > data
> > > -----
> > > 1
> > > 2
> > > 3
> > > 4
> > > 5
> > > 6
> > > 7
> > >
> > >
> > >  SELECT t.fields FROM table t WHERE data NOT IN (SELECT t2.data FROM table
> > >  t2 WHERE some_whereclause);
> > >
> > > it will select these rows which ones are not in the subquery. but you can
> > > do it simply by getting the negate of the whereclause...
> > >
> > >
> > >  Is it possible to have this result (interval of 3)?
> > >
> > > result
> > > ------
> > > 1
> > > 4
> > > 7
> > >
> > >
> > >  i don't see what you mean. please describe it.
> > >
> > >
> > >  thanks,
> > > kenneth
> > >
> > > --
> > >
> > >
> > >
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> > >
> > >
> > >
> > >  Bye,
> > >
> > > Gergely Czuczy
> > > mailto: phoemix(at)harmless(dot)hu
> > > PGP: http://phoemix.harmless.hu/phoemix.pgp
> > >
> > > "Wish a god, a star, to believe in,
> > > With the realm of king of fantasy..."
> > >
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> > >
> > >
> > >
> > >
> > > --
> > > [IMAGE]
> > >
> > >
> >
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>
>
> Bye,
>
> Gergely Czuczy
> mailto: phoemix(at)harmless(dot)hu
> PGP: http://phoemix.harmless.hu/phoemix.pgp
>
> "Wish a god, a star, to believe in,
> With the realm of king of fantasy..."
>

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Subject: Re: help on SQL
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