2. The computer-implemented method of claim 1 , wherein the step of determining whether the part of the expression in the query is equivalent to a defining expression for a virtual column comprises: determining whether the part of the expression in the query is logically equivalent to the defining expression for the virtual column.
2. The computer-implemented method of claim 1 , wherein the step of determining whether the part of the expression in the query is equivalent to a defining expression for a virtual column comprises: determining whether the part of the expression in the query is logically equivalent to the defining expression for the virtual column. 3. The computer-implemented method of claim 2 , wherein determining whether the part of the expression in the query is logically equivalent to the defining expression for the virtual column is based at least in part on associative, commutative, and distributive properties of the part of the expression and the defining expression for the virtual column.