摘要： 1.派生表(derived table)select YEAR(orderdate) as orderyear, COUNT(distinct custid) as numcustsfrom Sales.Ordersgroup by YEAR(orderdate);内联别名select orderyear, COUNT(distinct custid)from (select YEAR(orderdate)as orderyear, custid from Sales.Orders) as Dgroup by orderyear外部命名select orderyear, COUNT(disti 阅读全文