list all daily flights between boston and oakland and between oakland and boston using delta airlines 
return flights ;return #1 on delta airlines ;return #2 from boston  ;return #3 to  oakland  ;return #4 that  are daily ;return #2 from oakland  ;return #6 to  boston  ;return #7 that  are daily ;return #5 ,  #8
['select', 'filter', 'filter', 'filter', 'filter', 'filter', 'filter', 'filter', 'union']