Question

var orders =
    from c in customers
    from o in c.Orders
    where o.Total < 500.00M
    select new { c.CustomerID, o.OrderID, o.Total };

What is the difference between using 2 from clause and making inner join? Which one do I use? And When?

Answer 1

This will create the join for you. If you are using LINQ to SQL you can to a .ToString() on orders and you will see the generated SQL statement. If these were from two different sets it would create a cross join but because it is a child relation it will create the correct inner join for you.