实现子查询关联

 WhereClip w=Customers._.CustomerID==Orders._.CustomerID;

var t = DBUtility.DB.From<Customers>().RightJoin<Orders>(DBUtility.DB.From<Orders>().Where(Orders._.CustomerID == "QUICK"), "Orders", w).LeftJoin<Employees>(Orders._.EmployeeID==Employees._.EmployeeID);

先查询主表orders过滤出来一部分列表，然后从表customers右关联orders这样 形成查询的结果