A Comprehensive Survey of Join Techniques in Relational Databases

Equijoin between two relations is one of the basic operations in relational database and a large volume of research have been devoted to it. However, in recent years, there hasn't been a survey which objectively compares a wide spectrum of various join techniques in their relative performances. This survey compares performance and practicality between various join techniques. Main criteria for performance comparisons are disk I/Os. For comparing of practicality, criteria used are easiness and exibility of implementation. When comparing join techniques, each join technique is evaluated in its full potential, which means that if other techniques are available to enhance this join technique while retaining the main philosophy of it, the later techniques are applied. The main contribution of the paper is that it connrms the believe that no dra-matical performance improvement of three major join techniques (nested loops, sort-based, and hash based) of relational database can be made. The future of join performance improvement in relational database systems lies in more radical approach: parallel join, join index, composite index, and layered database.