Mark
Thank you very much for explanation. Now I understood the
case.
+0 is nothing at statment.
It is used only for Oracle does not
use the index.
Regards.
Eriovaldo
--------- Mensagem Original --------
De:
"Mark Richard" <mrichard@transurban.com.au>
Para: "Multiple
recipients of list ORACLE-L" <ORACLE-L@fatcity.com>
Assunto: Re:
Resource for index
Data: 14/10/03 22:32
The "+0" is simple arithmetic... Since the value is a number
they add zero
to the value to trick the optimisor into thinking the index
is useless
without actually changing the value. I guess alternatives
would be *1
(multiply by one), /1 (divide by one) and -0 (subtract zero).
For text
based columns the use of ||'' (append an empty string) achieves
a
practically identical
result.
"Eriovaldo
Andrietta" To: Multiple
recipients of list ORACLE-L
<ORACLE-L@fatcity.com>
<eca@siteplanet.c cc:
om.br>
by:
ml-errors@fatcity
.com
15/10/2003 11:44
Please
respond to
ORACLE-L
Dear Stephane,
At
first, my apologize by the word "Resource", it was the first word that
I
found out and wrote it.
The case is that this command +0 , you
can put it in the sentence line of
where and the sintaxe is
correct.
Oracle executes the statment and don't gives error
message.
My doubt is : What this +0 does in the sql ?
Imagine a
column unindexed that you can not create a index, because it will
do a
bad performance in all the system, you can use +0 that it will break
the
index . It is what i eard.
But i am searching about this +0 and until
now, i didn't find out nothing
about it.
For me it doesn't
exist.
Did you do a test ?
You can put it at the statment that
will run , normaly.
And more, if you to use explain plan the table
(unindexed) will have a FULL
TABLE SCAN.
So, I ask :
What is
this +0 ? Resource or not , it is my hard
doubt.
Regards
Eriovaldo
----- Original Message
-----
To: "Multiple recipients of list ORACLE-L"
<ORACLE-L@fatcity.com>
Sent: Monday, October 13, 2003 4:04
PM
> > Friends :
> >
> > I have a part of
statment as below :
> >
> > select column1 from
table1
> > where column1 = v_parameter;
> >
> >
The column1 is not indexed, so the table full scan will
be
executed.
> > Right?
> > Well, I would like to know
if anyone knows the resource :
> >
> > select column1 from
table1
> > where column1 = v_parameter +0
> >
> >
What does it mean (+0).
> > What kind of resource is it ?
>
> What does it do ?
> >
> > Best Regards
>
>
> > Eriovaldo
>
> Eriovaldo,
>
> Don't
understand too well what you mean by 'resource'. One of the
> most
cunning performance tips of yore was to either concatenate an empty
>
string to a string or date column or add a zero to a number column
to
> prevent the RBO from using an index on this column (BTW it's a
trick
> which can still be useful at times) when this index was known
to be not
> very selective.
> Quite obviously, applying this to
the constant part of an equality is
> totally pointless. And since the
column is unindexed, it wouldn't have
> much utility either on the
other side of the equality.
> Another case of ill-digested and
ill-understood trick.
>
> --
> Regards,
>
>
Stephane Faroult
> Oriole Software
> --
> Please see the
official ORACLE-L FAQ: http://www.orafaq.net
> --
>
Author: Stephane Faroult
> INET: sfaroult@oriole.com
>
>
Fat City Network Services -- 858-538-5051 http://www.fatcity.com
> San Diego,
California -- Mailing list and web hosting services
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Received on Wed Oct 15 2003 - 07:49:25 CDT
