Re: Indexes

From: Peter McKenzie <pemmck_at_ibm.net>
Date: 1997/07/24
Message-ID: <5r781h$qmp$1@marri.bs.wa.gov.au>#1/1

You can index a column which contains nulls but when you go looking for a record with a null in that column it won't use the index. This can be very useful if you have millions of records and you only want to access the few records where the column is not null. Your index will be small as none of the records with nulls will be included.

As far as a composite index goes you will get some use out of it as long as the first indexed column is not null for the cases you wish to retrieve. Tomm Carr wrote in article <33D4DE6A.5BC0_at_geocities.com>...
>Brad Worsfold wrote:
>>
>> If I want to create a composite index on two columns, will Oracle Index
a
>> row if one
>> of the columns is optional? Meaning that one column has a value, the
other
>> is null???
>
Received on Thu Jul 24 1997 - 00:00:00 CDT