There are several query models for accessing data from two or more tables in a relational database. Two models that have been observed are cross product and subset query, since those models can be used to produce same query result. To get an optimal system performance, it is needed to find the best model in specific conditions. By using Borland Delphi version 6 software program and Interbase version 6 as database system, the researcher was trying to prove the optimization query theory with heuristic model. The theory says that one method to optimize a query is by changing the cross product model into subset query.