What is first names of the top 5 staff who have handled the greatest number of complaints?
return staff ;return complaints handled of #1 ;return number of  #2 for each #1 ;return the  5 highest of #3 ;return #1 where #3 is equal to any of #4 ;return the  first names of #5
['select', 'project', 'group', 'aggregate', 'comparative', 'project']