How many people, in millions, did union membership expand between 1940 and 1945?
return union membership ;return people of #1 ;return #2 in  1940 ;return #2 in  1945 ;return number of  #3 ;return number of  #4 ;return difference of #6 and  #5 in  millions
['select', 'project', 'filter', 'filter', 'aggregate', 'aggregate', 'arithmetic']