A metadata extraction system executes a query against a database on a data storage device connected to a computer. Initially, the query is modified to replace one or more selected clauses with a false clause. The modified query with the false clause is executed. Metadata is retrieved from the result set obtained by executing the modified query. The metadata is used to obtain column types, which are converted to Java.TM. types. Then, a SQLJ iterator is generated, which has parameters for the Java.TM. types.