list all daily flights between boston and oakland as well as boston and oakland using american airline 
return flights ;return #1 from  boston ;return #2 to oakland  ;return #1 to boston ;return #4 from  oakland  ;return #3 , #5 ;return all daily of #6 ;return #7 on  american airlines
['select', 'filter', 'filter', 'filter', 'filter', 'union', 'project', 'filter']