1. A computer-implemented method for use in evaluating queries, the method comprising: receiving a query that includes an expression; determining whether a part of the expression in the query is equivalent to a defining expression for a virtual column, wherein a DBMS defines the virtual column as containing results of the defining expression, wherein the virtual column comprises at least one data value computed from the defining expression; in response to determining that the part of the expression is equivalent to the defining expression for the virtual column, modifying the query to generate a modified query, wherein the step of modifying the query comprises replacing, in the query, the part of the expression with the virtual column; and processing the modified query.