Method for transforming SQL queries

摘要

A computer-implemented method for transforming an SQL query comprising a WHERE clause having nested SELECT expressions. The expression in the WHERE clause being transformed by the iterative application of rules to comprise ThereExists expressions and associated truth-value expressions. Further transforming the expression to form a truth expression having the IS operator and iteratively applying further rules to translate 3-valued logic to 2-valued logic. Carrying out a further transformation to remove NOT expressions from the expression and to remove any ThereExists expressions so as to define an expression in 2-valued logic with simplified SELECT expressions.