Question on Indexing

[tamilselvan]

I would go for bitmap index.

The reasons:

1 Since the table gets 100 rows only every month, it tells that it is a DSS/DW system, definitely not a OLTP system.
2 The CREDIT_RATING column takes only 10 values. Assume they are all distributed evenly, then 'BAD' and 'F' may have 1 Million rows. And you are going to read 20 % of the rows from the table.
3 The column credit_rating is not "updated frequently". So no issue of locking.
4 The bitmap index is going to consume less space than the b-tree index.
5 Obviously the where clause will be like "CREDIT_RATINGS = 'BAD' or CREDIT_RATINGS = 'F'. Bitmap index works very well with LOGICAL OR conditions compared to b-tree index. For this reason alone, I would like to opt for bitmap index.

Tamil