Re: Select count(*) in Oracle and MySQL

On Oct 10, 4:14 am, "Shakespeare" <what..._at_xs4all.nl> wrote:
> "Shakespeare" <what..._at_xs4all.nl> schreef in berichtnews:470c859a$0$240$e4fe514c_at_news.xs4all.nl...
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> > "DA Morgan" <damor..._at_psoug.org> schreef in bericht
> >news:1191949360.256259_at_bubbleator.drizzle.com...
> >> richard.drouill..._at_gmail.com wrote:
> >>> On Sep 19, 2:40 pm, Occidental <Occiden..._at_comcast.net> wrote:
> >>>> I have a table with about 250M rows, implemented in both Oracle and
> >>>> MySQL.
> >>>> Select count(*) in MySQL is effectively instantaneous, presumably
> >>>> because it accesses some internal count that is maintained by the
> >>>> DBMS. The same query in Oracle takes about 6 minutes, pretty obviously
> >>>> becasue it counts rows. The Oracle table should have been set up with
> >>>> a primary key, but wasn't. The MySQL table has no primary key either.
> >>>> Any comments?
>
> >>> Oracle recommends using count(rowid) instead of count(*) for
> >>> performance reasons, I think you'll find this much faster.
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> >>>http://www.thewellroundedgeek.com/2007/09/most-people-use-oracle-coun...
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> >>> - Rich
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> >> Oracle doesn't recommend it ... you do. And in doing so you are
> >> incorrect.
>
> >> You should remove the recommendation from the website.
> >> --
> >> Daniel A. Morgan
> >> University of Washington
> >> damor..._at_x.washington.edu (replace x with u to respond)
> >> Puget Sound Oracle Users Group
> >>www.psoug.org
>
> > In 11g, there seem to be differences in performance with count(*) and
> > count(1), but only in rare cases like after adding a column to a view,
> > IIRC. Have seen some article about that, I'll try to look it up (but maybe
> > this WAS the quoted article). Count(rowid) is a bad idea for views BTW.
>
> > Shakespeare
>
> And here's the article. Not a perfomance issue, but still different
> behaviour:http://www.pythian.com/blogs/627/oracle-11g-unexpected-difference-bet...
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> Shakespeare

The blog entry Rich linked to is in fact his own posting; what is interesting is that in the blog he correctly identifies the book "Oracle Press Book: Oracle 10g: SQL" as the source, while here he attributes this "fact" to Oracle.

Brian Received on Wed Oct 10 2007 - 07:44:51 CDT