Oracle-L: Re: ** bitmap index for lot of nulls

From: Tanel Poder <tanel.poder.003_at_mail.ee>
Date: Mon, 04 Aug 2003 10:19:24 -0800
Message-ID: <F001.005C8D67.20030804101924@fatcity.com>

Hi!

Bitmap indexes are suited best for low cardinality columns in tables which are read only, such is gender, marital status or similar (a bitmap is needed for every different value). Since your non-null rows are unique, bitmap index isn't good choice.

Note that a regular single column index won't index any nulls. (In your 95% case it's not a problem, because if you'd search nulls, a table scan would be cheaper anyway, but if you want nulls to get indexed, you could create a composite index with your column + another not null column).

Tanel.

Original Message ----- From: A Joshi To: Multiple recipients of list ORACLE-L Sent: Monday, August 04, 2003 8:49 PM Subject: ** bitmap index for lot of nulls

Hi,
I am creating an index on a column that is null in most (over 95%) of the rows. In the rest of the rows it is expected to be unique. Is bitmap index suited for this? Thanks You.

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Author: Tanel Poder
INET: tanel.poder.003_at_mail.ee

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