Bitmap indexes can substantially improve performance of queries with the following characteristics:
- The WHERE clause contains multiple predicates on low- or medium-cardinality columns
- The individual predicates on these low- or medium-cardinality columns select a large number of rows
- Bitmap indexes have been created on some or all of these low- or medium-cardinality columns
- The tables being queried contain many rows
You can use multiple bitmap indexes to evaluate the conditions on a single table. Bitmap indexes are thus highly advantageous for complex ad hoc queries that
contain lengthy WHERE clauses. Bitmap indexes can also provide optimal performance for aggregate queries and for optimizing joins in star schemas.