Unnesting and Optimization Techniques for Extended-sql Queries Containing Generalized Quantiiers

Relational database systems do not eeectively support complex queries containing quantiiers (quanti-ed queries). Quantiied queries are becoming increasingly important in decision support applications in general, and health-care information systems in particular. Recently, it has been shown that generalized quantiiers provide an eeective way of expressing such queries naturally, and that generalized quantiiers can be eeciently supported in query processors. In this paper, we present unnesting and optimization techniques for an extended-SQL language, that supports generalized quantiier constructs, to translate extended-SQL queries to algebraic expressions. We introduce a new algebraic operator that captures the operational semantics of a wide range of generalized quantiiers. Furthermore, our optimization technique can also be applied during the unnesting of conventional nested SQL queries.