Correction to "Optimal Query Processing for Distributed Database Systems"
Wesley W. Chu, Paul Hurley · IEEE Transactions on Computers · 1983
In the above paper1, Theorem 1 is not true in general. The purpose of Theorem 1 was to reduce the number of feasible query trees by determining the optimal positions of unary operations in a given query tree. In fact, Theorem I is true only if the processing cost of a unary operation is independent of the volume of input data.