METHOD AND APPARATUS FOR INCREMENTAL REFRESH OF SUMMARY TABLES IN A DATABASE SYSTEM

A method and apparatus are provided for performing deferred incremental refresh of summary tables that are derived from two or more base tables. Incremental refresh is performed by assigning a hypothetical load sequence to the base tables of the summary table. For each base table that contains new data that affects the summary table, a join is performed between (1) the new data in the base table, (2) the pre-update state of base tables that follow the base table in the hypothetical load sequence, and (3) the post-update state of base tables the precede the base table in the hypothetical load sequence. The results of the join are then merged with the existing summary table to refresh the summary table. According to one aspect of the invention, efficiency is improved by performing the joins for the various base tables in parallel.