rticular role will have the sum
   of privileges granted directly to it, privileges granted to any role it
   is presently a member of, and privileges granted to
   <code class="literal">PUBLIC</code>.  Thus, for example, revoking <code class="literal">SELECT</code> privilege
   from <code class="literal">PUBLIC</code> does not necessarily mean that all roles
   have lost <code class="literal">SELECT</code> privilege on the object: those who have it granted
   directly or via another role will still have it