This document contains a comparison of Oracle, MySQL and PostgreSQL databases in the context of selection of a DBMS for ALICE experiment. One of the co-authors (W.Peryt), after his presentation on databases, was asked by the Technical Board at its meeting held at CERN on December 7-th 2000 to prepare such a document. This analysis was carried out by Warsaw database group from WUT, working for ALICE. We have taken the following approach: first of all we determined what features of DBMS are important from the point of view of such a large experiment.