1. A computer-implemented method to generate an online analytical processing (OLAP) query for data aggregated in a cube, the cube having a plurality of dimensions, each of the plurality of dimensions including a hierarchy of members, the method comprising: receiving a report specification against a hierarchy of the cube; identifying a first set among the members of the hierarchy, wherein the first set comprises members projected by the report specification that have a descendant at a lowest level of the hierarchy; identifying a second set among the members of the hierarchy, distinct from the first set, wherein the second set comprises members projected by the report specification that do not have any descendant at the lowest level of the hierarchy; and generating the OLAP query from the report specification and by operation of one or more computer processors, wherein the OLAP query joins the first set with the second set by a union operation.