Bitmap Indexes

When creating a bitmap index is it better to create individual bitmaps for each field OR group the fields together?

For example:
Table BOB1

Field1		varchar(3),
Field2		varchar(2),
Field3		varchar(4),
Field4		varchar(7),
Field5		number(11,2)

Create bitmap index b_bob_1
  on BOB1 (
  Field1);
Create bitmap index b_bob_2
  on BOB1 (
  Field2);
Create bitmap index b_bob_3
  on BOB1 (
  Field3);
Create bitmap index b_bob_4
  on BOB1 (
  Field4);
--------- OR -------------
Create bitmap index b_bob_1
  on BOB1 (
  Field1,Field2,Field3,Field4);

Typical searches may reference any number of the fields in varying order. Usually Field1 and Field2 are first, but then the next field in the search could be either Field3 or Field4.

So which method is best? Oh, this is a Data Warehouse type environment.

Thanks,
Daniel Received on Wed Apr 07 1999 - 13:59:21 CDT