SelectQuery qryCustomer = OQL

  .Select(NW.Customer.CustomerID)

  .From(NW.Customer)

  .Where(NW.Customer.ContactTitle == "Owner");

UpdateQuery updOrder = OQL

  .Update(NW.Order)

  .Set(NW.Order.ShippedDate, DateTime.Now.AddDays(20))

  .Where(NW.Order.CustomerID.In(qryCustomer));

The SQL statements generated as follows (taking SQL Server as an example)

UPDATE

  [Orders]

SET [Orders].[ShippedDate] = '2005-10-1 16:16:16'

WHERE

  [Orders].[CustomerID] IN

    (

      SELECT [Customers].[CustomerID]

      FROM [Customers]

      WHERE

        [Customers].[ContactTitle] = 'Owner'

    )