Show the 3 counties with the smallest population.
return counties ;return population of #1 ;return #1 where #2 is lowest ;return #1 besides  #3 ;return #4 where #2 is lowest ;return #4 besides  #5 ;return #6 where #2 is lowest ;return #3 ,  #5 ,   #7
['select', 'project', 'superlative', 'discard', 'superlative', 'discard', 'superlative', 'union']