Oracle-L: RE: NVL and index usage

From: Jamadagni, Rajendra <Rajendra.Jamadagni_at_espn.com>
Date: Thu, 02 Jan 2003 11:11:14 -0800
Message-ID: <F001.00525EC9.20030102111114@fatcity.com>

Thanks Tom and everyone ...

as I mentioned they plan to use it as follows ...

and nvl(new_column,'A') = nvl(some_value,'A')

So I asked them to see the possibility of creating the column with a DEFAULT VALUE of 'A' so the where clause can be written as

and new_column = nvl(some_value, 'A')

which I think is better and based on all your input, I am sure it will be. Finally it will be their call. When apps stop using indexes, they will call us though (with the standard question 'Did we run stats collection today?')

Raj

Rajendra Jamadagni MIS, ESPN Inc. Rajendra dot Jamadagni at ESPN dot com
Any opinion expressed here is personal and doesn't reflect that of ESPN Inc.

QOTD: Any clod can have facts, but having an opinion is an art!

-----Original Message-----
Sent: Thursday, January 02, 2003 1:51 PM To: Multiple recipients of list ORACLE-L

Raj,

the index will not be used.

think about it.

for those records that do not have a value (are null) for the indexed column - there is not an entry in the index - so they can not be evaluated to return a row.

secondly, even if all rows were represented in the index - why perform two queries - one for the index, and then one for the table - to evaluate whether to use the row in the query?

either way, it would not work properly.

that's why Oracle gave us function based indexes - so that we could use a function and get fast results from a large table.

hope this helps.

Tom Mercadante
Oracle Certified Professional

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Author: Jamadagni, Rajendra
  INET: Rajendra.Jamadagni_at_espn.com

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Received on Thu Jan 02 2003 - 13:11:14 CST