尝试在 IF 语句中使用函数参数时出错

Question

我有以下CREATE FUNCTION：

CREATE FUNCTION ufnTotalSales (@StartDate datetime, @EndDate datetime = GETDATE(), @FoodName nvarchar(50) = '')
RETURNS TABLE
AS
    RETURN
    (
        IF @FoodName = '';
        BEGIN
            SELECT f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales FROM Food f, OrderFoodRel ofr
            WHERE (Date_Time BETWEEN @StartDate AND @EndDate)
        END

        ELSE
        BEGIN
            SELECT f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales FROM Food f, OrderFoodRel ofr
            WHERE (Date_Time BETWEEN @StartDate AND @EndDate) AND @FoodName = FoodName
        END
    );

第一个错误发生在@EndDate datetime = GETDATE()，它显示Incorrect syntax near '()'。如果用户选择使用默认值，我正在尝试为@EndDate 参数分配当前datetime 的默认值，但不知何故我得到了错误。

第二个错误发生在我在IF ... ELSE 块中使用的所有参数（@FoodName、@StartDate 和@EndDate）。它说我Must declare the scalar variable "@..."。它是一个参数而不是一个标量变量，我该如何解决这个问题？

这个函数的想法是返回食品的总销售额，有两个选项：一个是名称为 X 的食品从某个日期到另一个日期的总销售额，如果您指定了食品名称；和两个是从一个日期到另一个日期的食品总销售额，不考虑食品名称。

Answer 1

这个函数有几个问题

首先，您不能将默认值分配给函数您不能在函数内使用IF .. ELSE 其次。表Food 和OrderFoodRel 不是JOINed。你在这里做一个交叉连接

它不喜欢getdate()作为默认值，你可以将@EndDate设置为NULL，并在@EndDate上使用ISNULL()

这将创建函数。我假设这 2 个表与 FoodID 相关联

CREATE FUNCTION ufnTotalSales 
(
    @StartDate datetime,  
    @EndDate   datetime     = NULL, 
    @FoodName  nvarchar(50) = ''
)
RETURNS TABLE
AS
    RETURN
    (
        SELECT  f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales 
        FROM    Food f
                INNER JOIN OrderFoodRel ofr on  f.FoodID    = ofr.FoodID
        WHERE   Date_Time BETWEEN @StartDate AND ISNULL(@EndDate, GETDATE())
        AND     (
                    @FoodName   = ''
                OR  f.FoodName  = @FoodName
                )
    );
GO

所以要在输入上使用默认值，需要使用关键字default

select  *
from    dbo.ufnTotalSales('2018-10-01', default , default)

Answer 2

使用下面的函数

CREATE FUNCTION ufnTotalSales 
(  @StartDate datetime, 
   @EndDate datetime, 
   @FoodName nvarchar(50)
)
RETURNS TABLE
AS
    RETURN
    (
        SELECT f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales 
        FROM Food f
        JOIN OrderFoodRel ofr on f.FoodID = ofr.FoodID
        WHERE (Date_Time BETWEEN @StartDate AND ISNULL(@EndDate,GETDATE())) 
         AND ISNULL(@FoodName,'') = FoodName

    );

Answer 3

您不能在 ITVF 中使用过程逻辑，而只能使用某种返回结果集的查询。

参考：https://docs.microsoft.com/en-us/sql/t-sql/statements/create-function-transact-sql?view=sql-server-2017

希望以下内容与您正在寻找的内容接近：

CREATE FUNCTION ufnTotalSales
(
  @StartDate datetime
  , @EndDate datetime
  , @FoodName nvarchar(50)
)
RETURNS TABLE
AS
RETURN
  SELECT f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales FROM Food f, OrderFoodRel ofr
  WHERE (Date_Time BETWEEN @StartDate AND coalesce(@EndDate,getdate()))
  and coalesce(@FoodName,'') = ''
  union all
  SELECT f.FoodID, FoodName, (FoodPrice * Quantity) AS TotalSales FROM Food f, OrderFoodRel ofr
  WHERE (Date_Time BETWEEN @StartDate AND coalesce(@EndDate,getdate()))
  AND coalesce(@FoodName,'') = FoodName