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how about
select count(distinct s.specimen_id) from specimens sp INNER JOIN
sequences s
on s.specimen_id = sp.id;
>>> Julien <jcigar@[EMAIL PROTECTED]
> 2008-03-13 17:27 >>>
mmh no because it's a one to many relation (a specimen can have more
than one sequence) :
muridae=> select count(sp.id) from specimens sp INNER JOIN sequences s
on s.specimen_id = sp.id;
count
-------
1536
(1 row)
Time: 81.242 ms
muridae=> select count(sp.id) from specimens sp where sp.id in (select
specimen_id from sequences group by specimen_id);
count
-------
1431
(1 row)
Time: 81.736 ms
muridae=>
(of course this is a bad example, because I could just do: select
count(specimen_id) from sequences group by specimen_id;, but in my
application I have more fields coming from specimens of course)
Julien
On Thu, 2008-03-13 at 15:12 +0100, Bart Degryse wrote:
> I think that just
> select count(sp.id) from specimens sp INNER JOIN sequences s on
> s.specimen_id = sp.id;
> should be enough
>
> >>> Julien <jcigar@[EMAIL PROTECTED]
> 2008-03-13 17:10 >>>
> If I understood well the query plan, the planner optimize the
> IN(SELECT ...) version with a JOIN (line 19-20 of the first paste) :
>
> -> Hash IN Join (cost=240.95..4011.20 rows=1436 width=4) (actual
> time=93.971..201.908 rows=1431 loops=1)
> Hash Cond: ("outer".id = "inner".specimen_id)
>
> so I guess that :
>
> select count(sp.id) from specimens sp where sp.id in (select
> specimen_id
> from sequences);
>
> is almost the same as :
>
> select count(sp.id) from specimens sp INNER JOIN (select specimen_id
> from sequences GROUP BY specimen_id) as foo on foo.specimen_id =
> sp.id;
>
> ?
>
> Thanks,
> Julien
>
> On Thu, 2008-03-13 at 14:46 +0100, Bart Degryse wrote:
> > The chapter on indexes in the manual should give you a pretty good
> > idea on the why.
> > IN and EXISTS are not the only possibilities, you can also use
inner
> > or outer joins.
> > Which solution performs best depends on the data, the database
> > version, the available indexes, ...
> >
> > >>> Julien <jcigar@[EMAIL PROTECTED]
> 2008-03-13 15:47 >>>
> > Hello,
> >
> > Does anyone has an idea why sometimes:
> > - select ... where ... in (select ...)
> > is faster than :
> > - select ... where ... exists(select ...)
> > and sometimes it's the opposite ?
> >
> > I had such a situation, I've pasted the queries on:
> > http://rafb.net/p/KXNZ6892.html
and http://rafb.net/p/jvo5DO38.html
> >
> > It's running PostgreSQL 8.1 with an effective_cache_size of 30000.
> >
> > specimens.id is the primary key and there are indexes on
> > sequences(specimen_id) and specimen_measurements(specimen_id)
> >
> > Is there a general "rule" to know when to use the in() version and
> > when
> > to use the exists() version ? Is it true to say that the exists()
> > version is more scalable (with many rows) than the in() version
> (from
> > the little tests I made it seems the case) ?
> >
> > Thanks,
> > Julien
> >
> > --
> > Julien Cigar
> > Belgian Biodiversity Platform
> > http://www.biodiversity.be
( http://www.biodiversity.be/
)
> > Université Libre de Bruxelles (ULB)
> > Campus de la Plaine CP 257
> > Bâtiment NO, Bureau 4 N4 115C (Niveau 4)
> > Boulevard du Triomphe, entrée ULB 2
> > B-1050 Bruxelles
> > Mail: jcigar@[EMAIL PROTECTED]
> > @[EMAIL PROTECTED]
http://biobel.biodiversity.be/person/show/471
> > Tel : 02 650 57 52
> >
> >
> > --
> > Sent via pgsql-sql mailing list (pgsql-sql@[EMAIL PROTECTED]
)
> > To make changes to your subscription:
> > http://www.postgresql.org/mailpref/pgsql-sql
> >
> --
> Julien Cigar
> Belgian Biodiversity Platform
> http://www.biodiversity.be
( http://www.biodiversity.be/
)
> Université Libre de Bruxelles (ULB)
> Campus de la Plaine CP 257
> Bâtiment NO, Bureau 4 N4 115C (Niveau 4)
> Boulevard du Triomphe, entrée ULB 2
> B-1050 Bruxelles
> Mail: jcigar@[EMAIL PROTECTED]
> @[EMAIL PROTECTED]
http://biobel.biodiversity.be/person/show/471
> Tel : 02 650 57 52
>
>
> --
> Sent via pgsql-sql mailing list (pgsql-sql@[EMAIL PROTECTED]
)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-sql
>
--
Julien Cigar
Belgian Biodiversity Platform
http://www.biodiversity.be
( http://www.biodiversity.be/
)
Université Libre de Bruxelles (ULB)
Campus de la Plaine CP 257
Bâtiment NO, Bureau 4 N4 115C (Niveau 4)
Boulevard du Triomphe, entrée ULB 2
B-1050 Bruxelles
Mail: jcigar@[EMAIL PROTECTED]
@[EMAIL PROTECTED]
http://biobel.biodiversity.be/person/show/471
Tel : 02 650 57 52
--
Sent via pgsql-sql mailing list (pgsql-sql@[EMAIL PROTECTED]
)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql
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<DIV>how about</DIV>
<DIV>select count(distinct s.specimen_id) from specimens sp INNER =
JOIN sequences s </DIV>
<DIV>on s.specimen_id =3D sp.id;<BR><BR><BR>>>> Julien
<jcigar@[EMAIL PROTECTED]
2008-03-13 17:27 >>><BR>mmh no because it's a one =
to many relation (a specimen can have more<BR>than one sequence)
:<BR><BR>m=
uridae=3D> select count(sp.id) from specimens sp INNER JOIN sequences =
s<BR>on s.specimen_id =3D sp.id;<BR>count <BR>-------<BR> 1536<BR>(1
=
row)<BR><BR>Time: 81.242 ms<BR>muridae=3D> select count(sp.id) from =
specimens sp where sp.id in (select<BR>specimen_id from sequences group by
=
specimen_id);<BR>count <BR>-------<BR> 1431<BR>(1 row)<BR><BR>Time:
=
81.736 ms<BR>muridae=3D> <BR><BR>(of course this is a bad example, =
because I could just do: select<BR>count(specimen_id) from sequences group
=
by specimen_id;, but in my<BR>application I have more fields coming from =
specimens of course)<BR><BR>Julien<BR><BR>On Thu, 2008-03-13 at 15:12 =
+0100, Bart Degryse wrote:<BR>> I think that just<BR>> select =
count(sp.id) from specimens sp INNER JOIN sequences s on<BR>>
s.specimen=
_id =3D sp.id;<BR>> should be enough<BR>> <BR>> >>> =
Julien <jcigar@[EMAIL PROTECTED]
2008-03-13 17:10 >>><BR>> If I
=
understood well the query plan, the planner optimize the<BR>> IN(SELECT
=
....) version with a JOIN (line 19-20 of the first paste) :<BR>> =
<BR>> -> Hash IN Join (cost=3D240.95..4011.20
rows=3D1436=
width=3D4) (actual<BR>> time=3D93.971..201.908 rows=3D1431
loops=3D1)<B=
R>> Hash Cond: =
("outer".id =3D "inner".specimen_id)<BR>> <BR>> so I guess that =
:<BR>> <BR>> select count(sp.id) from specimens sp where sp.id in =
(select<BR>> specimen_id<BR>> from sequences);<BR>> <BR>> is =
almost the same as :<BR>> <BR>> select count(sp.id) from specimens =
sp INNER JOIN (select specimen_id<BR>> from sequences GROUP BY =
specimen_id) as foo on foo.specimen_id =3D<BR>> sp.id;<BR>> <BR>>
=
?<BR>> <BR>> Thanks,<BR>> Julien<BR>> <BR>> On Thu, =
2008-03-13 at 14:46 +0100, Bart Degryse wrote:<BR>> > The chapter on
=
indexes in the manual should give you a pretty good<BR>> > idea on =
the why.<BR>> > IN and EXISTS are not the only possibilities, you =
can also use inner<BR>> > or outer joins.<BR>> > Which =
solution performs best depends on the data, the database<BR>> > =
version, the available indexes, ...<BR>> > <BR>> >
>>>=
Julien <jcigar@[EMAIL PROTECTED]
2008-03-13 15:47 >>><BR>> =
> Hello,<BR>> > <BR>> > Does anyone has an idea why =
sometimes:<BR>> > - select ... where ... in (select ...)<BR>> =
> is faster than :<BR>> > - select ... where ... exists(select =
....)<BR>> > and sometimes it's the opposite ?<BR>> > <BR>>
=
> I had such a situation, I've pasted the queries on:<BR>> > <A =
href=3D"http://rafb.net/p/KXNZ6892.html">http://rafb.net/p/KXNZ6892.html</A=
> and <A
href=3D"http://rafb.net/p/jvo5DO38.html">http://rafb.net/p/jvo5DO3=
8.html</A><BR>> > <BR>> > It's running PostgreSQL 8.1 with an
=
effective_cache_size of 30000.<BR>> > <BR>> > specimens.id is
=
the primary key and there are indexes on<BR>> >
sequences(specimen_id=
) and specimen_measurements(specimen_id)<BR>> > <BR>> > Is =
there a general "rule" to know when to use the in() version and<BR>> =
> when<BR>> > to use the exists() version ? Is it true to say =
that the exists()<BR>> > version is more scalable (with many rows) =
than the in() version<BR>> (from<BR>> > the little tests I made =
it seems the case) ?<BR>> > <BR>> > Thanks,<BR>> > =
Julien<BR>> > <BR>> > -- <BR>> > Julien Cigar<BR>> =
> Belgian Biodiversity Platform<BR>> > <A
href=3D"http://www.biodi=
versity.be/">http://www.biodiversity.be</A><BR>>
> Universit=C3=A9 =
Libre de Bruxelles (ULB)<BR>> > Campus de la Plaine CP 257<BR>> =
> B=C3=A2timent NO, Bureau 4 N4 115C (Niveau 4)<BR>> > Boulevard
=
du Triomphe, entr=C3=A9e ULB 2<BR>> > B-1050 Bruxelles<BR>> >
=
Mail: jcigar@[EMAIL PROTECTED]
>> > @[EMAIL PROTECTED]
<A
href=3D"http://biobel.biodi=
versity.be/person/show/471">http://biobel.biodiversity.be/person/show/471</=
A><BR>> > Tel : 02 650 57 52<BR>> > <BR>> > <BR>> =
> -- <BR>> > Sent via pgsql-sql mailing list
(pgsql-sql@[EMAIL PROTECTED]
)<BR>> > To make changes to your subscription:<BR>> > <A
=
href=3D"http://www.postgresql.org/mailpref/pgsql-sql">http://www.postgresql=
..org/mailpref/pgsql-sql</A><BR>> > <BR>> -- <BR>> Julien =
Cigar<BR>> Belgian Biodiversity Platform<BR>> <A
href=3D"http://www.b=
iodiversity.be/">http://www.biodiversity.be</A><BR>>
Universit=C3=A9 =
Libre de Bruxelles (ULB)<BR>> Campus de la Plaine CP 257<BR>> =
B=C3=A2timent NO, Bureau 4 N4 115C (Niveau 4)<BR>> Boulevard du =
Triomphe, entr=C3=A9e ULB 2<BR>> B-1050 Bruxelles<BR>> Mail: =
jcigar@[EMAIL PROTECTED]
>> @[EMAIL PROTECTED]
<A
href=3D"http://biobel.biodiversity.be/=
person/show/471">http://biobel.biodiversity.be/person/show/471</A><BR>>
=
Tel : 02 650 57 52<BR>> <BR>> <BR>> -- <BR>> Sent via =
pgsql-sql mailing list (pgsql-sql@[EMAIL PROTECTED]
)<BR>> To make changes
=
to your subscription:<BR>> <A
href=3D"http://www.postgresql.org/mailpref=
/pgsql-sql">http://www.postgresql.org/mailpref/pgsql-sql</A><BR>>
=
<BR>-- <BR>Julien Cigar<BR>Belgian Biodiversity Platform<BR><A
href=3D"http=
://www.biodiversity.be/">http://www.biodiversity.be</A><BR>Universit=C3=A9
=
Libre de Bruxelles (ULB)<BR>Campus de la Plaine CP 257<BR>B=C3=A2timent =
NO, Bureau 4 N4 115C (Niveau 4)<BR>Boulevard du Triomphe, entr=C3=A9e ULB
=
2<BR>B-1050 Bruxelles<BR>Mail: jcigar@[EMAIL PROTECTED]
>@[EMAIL PROTECTED]
<A
href=3D"http=
://biobel.biodiversity.be/person/show/471">http://biobel.biodiversity.be/pe=
rson/show/471</A><BR>Tel : 02 650 57 52<BR><BR><BR>-- <BR>Sent via =
pgsql-sql mailing list (pgsql-sql@[EMAIL PROTECTED]
)<BR>To make changes to =
your subscription:<BR><A
href=3D"http://www.postgresql.org/mailpref/pgsql-s=
ql">http://www.postgresql.org/mailpref/pgsql-sql</A><BR></DIV></BODY></HTML=
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