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Home -> Community -> Mailing Lists -> Oracle-L -> RE: NVL and index usage
Raj,
If they think that stats need to be collected every day for indexes to work then they obviously don't know much about Oracle... Either that or you have some incredibly volatile tables like a fully refreshed DSS or something. Ideally you should ask the developers which tables should be analyzed and how often. They should understand the movement of data although it sounds like they might not understand Oracle enough anyway. At least they have you looking out for them.
Regards,
Mark.
PS: Since the column is being added to an existing table remember that you will have to update existing rows as well as adding the default clause.
"Jamadagni,
Rajendra" To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
<Rajendra.Jamadagni cc:
@espn.com> Subject: RE: NVL and index usage
Sent by:
root_at_fatcity.com
03/01/2003 06:11
Please respond to
ORACLE-L
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
-----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 (See attached file: ESPN_Disclaimer.txt)
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