list number of people that can be carried on each type of plane that flies between pittsburgh and baltimore 
return flights ;return #1 from pittsburgh ;return #2 to  baltimore ;return #1 from baltimore ;return #4 to  pittsburgh ;return #3 ,  #5 ;return type of planes of  #6 ;return number of people that  can be carried of  #7
['select', 'filter', 'filter', 'filter', 'filter', 'union', 'project', 'project']