Bitmap Indexes

Platform - windows nt 4.0
Oracle - 7.3.4.0.0

I had created a bitmap index on a field which has a very low cardinality. I enabled all initialization parameters affected by the bitmap index. When I do a select which searches bitmap indexed column, the explain shows me that a full table scan was done.

create bitmap index rmn_x1 on secm(security_status);

select sec_no, sec_shortcode where security_status = 'C';

Rows Execution Plan

-------  ---------------------------------------------------
      0  SELECT STATEMENT   GOAL: CHOOSE