Abstract: A method and apparatus for processing star queries is provided. According to the method, a star query is transformed by adding to the star query subqueries that are not in the query. The subqueries are generated based on join predicates and constraints on dimension tables that are contained in the original query. The subqueries are executed, and the values returned by the subqueries are used to access one or more bitmap indexes built on columns of the fact table. The bitmaps retrieved for the values returned by each subquery are merged to create one subquery bitmap per subquery. An AND operation is performed on the subquery bitmaps, and the resulting bitmap is used to determine which data to retrieve from the fact table.

Abstract: Sort plus operations such as "group by" and "distinct" generally require sorting of the retrieved data before performing the sort plus operation. A method and apparatus is disclosed for executing a query specifying a sort plus operation without performing the sorting operation. A cost-based optimizer determines at least one execution path where the data is retrieved from a sorted source and the data is processed to satisfy the query without sorting. Execution costs are determined for the respective execution paths, and the execution path having the lowest overall execution cost is selected to process the query.

Abstract: A method and apparatus for processing count queries in a database system is provided. The database server determines whether it is possible for the target data specified in a count query to contain null values. If the target data cannot contain null values, the count query is converted into a count star query. Count star queries are executed by counting the number of records that store the target data without actually reading and evaluating the target data. If an index for the table that stores the target data exists, then the number of records are counted without accessing the table itself by counting record identifiers in the index. If the index is a bitmap index, the number of bits that are set in bitmaps from the index are counted without actually generating record identifiers from the bitmaps. Many processes are used to generate intermediate count values from the bitmaps. The intermediate count values are summed to produce a total count value.