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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Resource for index
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_at_fatcity.com>
<eca_at_siteplanet.c cc:
om.br> Subject: Re: Resource for index
Sent by:
ml-errors_at_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
> > 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_at_oriole.com > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB ORACLE-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). >
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