表类型

　　表类型简化了表变量的定义。通过创建表类型，可以把表的定义保存到数据库中，以后在定义表变量，存储过程和用户定义函数的输入参数时，就可以将表类型作为表的定义而重用。

下面的示例演示了如何通过表类型来简化表变量的定义，并且如何重用它。

USE TSQLFundamentals2008;GOIF TYPE_ID('dbo.OrderTotalsByYear') IS NOT NULL DROP TYPE dbo.OrderTotalsByYear;GO-- 创建表类型CREATE TYPE dbo.OrderTotalsByYear AS TABLE(    orderyear INT NOT NULL PRIMARY KEY,    qty INT NOT NULL);-- 通过表类型创建表变量，并且填充数据DECLARE @MyOrderTotalsByYear AS dbo.OrderTotalsByYear;INSERT INTO @MyOrderTotalsByYear( orderyear,qty )SELECT YEAR(orders.orderdate)AS orderdate,SUM(orderdetails.qty) AS qty FROM Sales.Orders AS ordersLEFT JOIN Sales.OrderDetails AS orderdetails ON orders.orderid = orderdetails.orderidGROUP BY YEAR(orders.orderdate);SELECT * FROM @MyOrderTotalsByYear;

查询结果：