Set Comparison Queries in SQL

Abstract

One of the most important promises of the relational data model has been that it frees the decision maker, the manager, from the necessity of resorting to an intermediary, the programmer, in retrieving information from the organization’s database in response to unanticipated needs. That promise is founded on the availability of very high-level relational query languages such as SQL. Unfortunately, the current specification of the SQL standard fails to support users adequately in formulating complex queries involving set comparison that tend to arise in on-line analytical processing (OLAP) situations. As pointed out by Rao et al. (1996): “SQL’s syntax is too restricted to express quantified queries. While SQL allows subqueries to form sets, the relationships that can be expressed over sets are limited, and must be written in awkward and complicated ways.” This chapter presents a systematic approach for teaching users how to formulate in SQL complex set comparison queries encountered in ad-hoc decision-making scenarios.