Green computing or Green IT is the environmentally responsible use of computers and related resources as well as the reduction of power resource consumption. In supporting green computing, this paper reports the results of an experiment that has been conducted which records the time taken and the energy consumed when running Join queries which retrieve all data from three relational databases of varying structures. The paper shares the experimental setup which includes the development of three differently designed database structures, the join queries to be tested as well as the datasets which are used in the experiment. Comparing the results of the join queries run on each of the three structures, there is no significant impact of a differently structured database on the amount of energy consumed by the queries if all data are retrieved. However, if the retrieved data are selective and come from indirectly linked tables, then the database structure does matter. © 2017 American Scientific Publishers. All rights reserved.