question: Which customers have both "On Road" and "Shipped" as order status? List the customer ids.
#1 return customers 
#2 return orders of #1 
#3 return statuses of #2 
#4 return #1 where #3 is On Road 
#5 return #1 where #3 is Shipped 
#6 return #1 in  both #4 and  #5 
#7 return customer ids of #6