What is the average, maximum, and minimum budget for all movies before 2000.
return movies ;return #1 before 2000 ;return budgets of #2 ;return average of #3 ;return maximum of #3 ;return minimum of #3 ;return #4 , #5 ,  #6
['select', 'filter', 'project', 'aggregate', 'aggregate', 'aggregate', 'union']