Provided are a computer implemented method, computer program product, and system for re-writing a query. A query including a query predicate is received. It is determined that the query predicate includes one column with an associated predicate mapper. An equivalent predicate is generated for the query predicate using the predicate mapper that provides a mapping from the one column to another column. A cost of the query with the equivalent predicate is evaluated. In response to determining that the cost of the query is optimal, the query is rewritten to replace the query predicate with the equivalent predicate.