Optimization of Single Expressions in a Relational Data Base System

This paper examines optimization within a relational data base system. It considers the optimization of a single query defined by an expression of the relational algebra. The expression is transformed into an equivalent expression or sequence of expressions that cost less to evaluate. Alternative transformations, and combinations of several transformations, are analyzed. Measurements on an experimental data base showed improvements, especially in cases where the original expression would be impracticably slow in its execution. A small overhead was incurred, which would be negligible for large data bases.