Watch the selectivity of the index if you use 'UNKNOWN' for a null value.
"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote:
>Oracle will not index null values (with the exception of bitmap indices). .
>This may mean that the optimiser will choose to do a full table scan rather
>than use an apparently appropriate index. Conversely you may fnd that
>indexes are far smaller and used more appropriately than if you filled the
>field with a placeholder value (like 'UNKNOWN').
>
>
>--
>Niall Litchfield
>Oracle DBA
>Audit Commission UK
>*****************************************
>Please include version and platform
>and SQL where applicable
>It makes life easier and increases the
>likelihood of a good answer
>
>******************************************
>"Steffen Ramlow" <s.ramlow_at_gmx.de> wrote in message
>news:a2hake$112tge$1_at_ID-54600.news.dfncis.de...
>> sample1:
>>
>> id col1 col2
>> ---------------
>> 1 v11 v12
>>
>>
>> versus:
>>
>> sample2:
>>
>> id col1 col2
>> ---------------
>> 1 v11 null
>> 1 null v12
>>
>>
>> there maybe indexes on the tabel, at least in column id
>>
>> where r the problems in sample2?
>>
>>
>
>
--
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Received on Tue Jan 22 2002 - 04:16:15 CST
