Bitmap indexes

[tatireddis]

Hi All:

I need a small clarification on Bitmap Indexes.


Example:

My table Structure.

Usage_type not null Primary key
Used_or_not null check (used_or_not in ('Y','N')

With this structure I acn insert a null value into Used_or_not
column.

But my queires or much based on used_or_not, The designer is not
accepting to change the column used_or_not to Not Null.
Previously they have created a normal index.
But now i want to change to Bitmap Index. Will the Null Value in
the column affect much of the performance of the Bitmap Index.

Pl. suggest me if Bitamp performance is degraded then what type
of index will help to increase the perfomance.


Regards

Srini

[gpsingh]

If the column is not highly update/delete then bitmap is a good choice.
Even if u have a batch updates and for most of the time it remains read only, even then u should go for bitmap.

Unique index on 1,2.
This shall a waste a lot of space, and also if the number of rows are very large and returned rows is also large it is goinf to wasteful.