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 table. 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 SQL.