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 <[EMAIL PROTECTED]>
<[EMAIL PROTECTED] cc:
om.br> Subject: Re: Resource for index
Sent by:
[EMAIL PROTECTED]
.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" <[EMAIL PROTECTED]>
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: [EMAIL PROTECTED]
>
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