How many days had both mean humidity above 50 and mean visibility above 8?
return days ;return mean  humidity of  #1 ;return mean  visibility of  #1 ;return #1 where  #2 is  higher than 50 ;return #1 where  #3 is  higher than 8 ;return #1 of  both #4 and #5
['select', 'project', 'project', 'comparative', 'comparative', 'intersection']