以下是一些示例,以便说明:
内联表值
CREATE FUNCTION MyNS.GetUnshippedOrders()
RETURNS TABLE
AS
RETURN SELECT a.SaleId, a.CustomerID, b.Qty
FROM Sales.Sales a INNER JOIN Sales.SaleDetail b
ON a.SaleId = b.SaleId
INNER JOIN Production.Product c ON b.ProductID = c.ProductID
WHERE a.ShipDate IS NULL
GO
多语句表值函数
CREATE FUNCTION MyNS.GetLastShipped(@CustomerID INT)
RETURNS @CustomerOrder TABLE
(SaleOrderID INT NOT NULL,
CustomerID INT NOT NULL,
OrderDate DATETIME NOT NULL,
OrderQty INT NOT NULL)
AS
BEGIN
DECLARE @MaxDate DATETIME
SELECT @MaxDate = MAX(OrderDate)
FROM Sales.SalesOrderHeader
WHERE CustomerID = @CustomerID
INSERT @CustomerOrder
SELECT a.SalesOrderID, a.CustomerID, a.OrderDate, b.OrderQty
FROM Sales.SalesOrderHeader a INNER JOIN Sales.SalesOrderHeader b
ON a.SalesOrderID = b.SalesOrderID
INNER JOIN Production.Product c ON b.ProductID = c.ProductID
WHERE a.OrderDate = @MaxDate
AND a.CustomerID = @CustomerID
RETURN
END
GO
使用一种类型(行内或多语句)是否比使用另一种类型更有优势?是否在某些情况下,一种方法比另一种更好,或者差异纯粹是语法上的?我意识到这两个示例查询正在执行不同的操作,但是我会以那种方式编写它们,是否有原因?
阅读它们和有关优点/差异的内容并没有真正被解释。