commonalties among them30. Microsoft SQL Server
supports Cube and Rollup.
• Comparisons: An article by Ralph Kimball and Kevin
Strehlo provides an excellent overview of the
deficiencies of SQL in being able to do comparisons that
are common in the business world, e.g., compare the
difference between the total projected sale and total
actual sale by each quarter, where projected sale and
actual sale are columns of a table31. A straightforward
execution of such queries may require multiple
sequential scans. The article provides some alternatives
to better support comparisons. A recent research paper
also addresses the question of how to do comparisons
among aggregated values by extending SQL32.