the creating and inserting data of the "usergroups" table is missing under the sql folder and should be completed in order to run the sample like expected.
The postgresql example has been updated not to require "usergroups" table anymore. There are other examples (e.g. join, jdbc_join) that show how to implement join operation.
The changes have been committed into the main repository: http://github.com/identity/penrose-server/commit/a035ba2934210afb80c8dd08d7309f4fd9e75196