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Home -> Community -> Mailing Lists -> Oracle-L -> Re: ** bitmap index for lot of nulls
Thanks Tanel. Point taken.
Related question : Since this table is going to have a lot of nulls for this indexed column how will it affect performance for insert in to the table. Is it safe to assume that there will be no performance impact as a result of this additional index. Thank You
Tanel Poder <tanel.poder.003_at_mail.ee> wrote: 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 -----
To: Multiple recipients of list ORACLE-L
Sent: Monday, August 04, 2003 8:49 PM
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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