Making Query Coding in SQL Easier by Implementing the SQL Divide Keyword

Abstract

Relational Algebra (RA) and structured query language (SQL) are supposed to have a bijective relationship by having the same expressive power. That is, each operation in SQL can be mapped to one RA equivalent and vice versa. Actually, this is an essential fact because in commercial database management systems, every SQL query is translated into equivalent RA expression, which is optimized and executed to produce the required output. However, RA has an explicit relational division symbol (÷), whereas SQL does not have a corresponding explicit division keyword. Division is implemented using a combination of four core operations, namely cross product, difference, selection, and projection. In fact, to implement relational division in SQL requires convoluted queries with multiple nested select statements and set operations. Explicit division in relational algebra is possible when the divisor is static; however, a dynamic divisor forces the coding of the query to follow the explicit expression using the four core operators. On the other hand, SQL does not provide any flexibility for expressing division when the divisor is static. Thus, the work described in this chapter is intended to provide SQL expression equivalent to explicit relational algebra division (with static divisor). In other words, the goal is to implement a SQL query rewriter in Java which takes as input a divide grammar and rewrites it to an efficient query using current SQL keywords. The developed approach could be adapted as front-end or wrapper to existing SQL query system.Users will be able to express explicit division in SQL which will be translated into an equivalent expression that involves only the standard SQL keywords and structure. This will turn SQL into more attractive for specifying queries involving explicit division.