Question on NULLs in index

Hi:

I have an index which is not getting used. Here is the situation.

select date_field_a
from table_one
where date_field_a IS NULL

I have an index on table_one(date_field_a)

i.e. create index my_index

      on table_one(date_field_a)

When I execute my select, it does a full table scan. I thought it should be using the index. I thought that there was always a 1-1 row relationship between an index it's associated table, and that NULLs in indexes were allowed. If that is right, my select should have used the index. However, since it did not, my thinking on this may be wrong.

I can work around not using the index. Indexing this date field will probably not be efficient anyways.

I would just like to know why the index isn't getting used. Is there something about NULLs in non-unique indexes that I am missing?

Thanks for any response.

Bill   Received on Mon Jul 13 1998 - 10:53:45 CDT