how many stops are on all flights from boston to san francisco that depart before 12 o'clock noon 
return flights ;return #1 from boston ;return #2 to  san francisco ;return #3 that  depart before 12 o'clock noon ;return stops on #4 ;return number of  #5 for each #4 ;return sum of #6
['select', 'filter', 'filter', 'filter', 'project', 'group', 'aggregate']