comparison two column of same row

Question

i want to Display the OrderID of all orders that where placed after all orders placed by Bottom-Dollar Markets.

i used the fllowing query

select 
    Orders.OrderID 
from 
    Orders 
where 
    Orders.OrderDate > (
        select 
            Orders.OrderDate 
        from 
            Orders 
        where 
            Orders.CustomerID = (
                select 
                    Customers.CustomerID 
                from 
                    Customers 
                where 
                    Customers.CompanyName='Bottom-Dollar Markets'
            ) 
        );

but it gives the error subquery returened more than one value

i am using northwind database

Answer 1

Both of your subqueries could return multiple rows, which isn't allowed when you're using a scalar comparison operation - > and =, respectively, in your case.

Try this instead:

select Orders.OrderID
from Orders
where Orders.OrderDate > (
  select max(Orders.OrderDate)
  from Orders
  where Orders.CustomerID in (
    select Customers.CustomerID
    from Customers
    where Customers.CompanyName='Bottom-Dollar Markets'
  )
);

You don't actually need to compare all orders since if the order of a customer is greater than the latest order placed by Bottom-Dollar Markets, then it follows it is also greater than earlier orders.

Alternatively this would work with a JOIN:

select Orders.OrderID
from Orders
where Orders.OrderDate > (
  select max(Orders.OrderDate)
  from Orders join Customers on Orders.CustomerID = Customers.CustomerID
  where Customers.CompanyName='Bottom-Dollar Markets'
);