In Mastering OLAP, "Cell-Level Security" (December 1999), I discussed OLAP Services' cell-level security capabilities and how an MDX expression lets you control which cells a user can access. When a user doesn't have access to a cell, OLAP Services returns the cell value #N/A. This month's MDX puzzle question is "How would you write an MDX query so the cells that you don't have access to return empty (null) values instead of #N/A?" Until next time, if you have ideas or questions for future colum...