user-defined scalar function to generate computed column

问题

I have databse having 2 tables i.e (Installment and InstallmentPlan). In the installment table there are number of columns. I want to add one new computed column name SurchargeCalculated (SC). The calculation for SC is this

SC = (Installment.Amount * Installment.days * (InstallmentPlan.InstPercentage /365 /100)) 

I have created user-defined function SurchargeCal having 3 parameters which are Amount, days and InstPercentage. The problem is that when i add computed column in installment table and call scalar function from there, the saclar func needs InstPercetage parameter of 2nd table (InstallmentPlan). I know recommended ways is to use view but that will complicate my problem as i am using installment table in C#.

Any help will be extremely appreciated.

My scalar function is

USE [myDB]
GO
/****** Object:  UserDefinedFunction [dbo].[SurchargeCal]    Script Date: 17/02/2020 2:21:15 PM 
******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
ALTER FUNCTION [dbo].[SurchargeCal] 
(
    -- Add the parameters for the function here
    @days as int,
    @amount as money,
    @surchargePerc as decimal
)
RETURNS decimal
AS
BEGIN
    -- Declare the return variable here
    DECLARE @result as decimal =0;

    -- Add the T-SQL statements to compute the return value here
    --SELECT <@ResultVar, sysname, @Result> = <@Param1, sysname, @p1>

        if  @days = 0
            set @result = 0
        else if (@days > 0 and @amount > 0)
            set @result = (@days * @amount * (@surchargePerc/ 365 / 100))
        else
            set @result = 0


    -- Return the result of the function
    RETURN @result

END

then below ADD table command XXXX is the problem

USE [myDB]
GO
ALTER TABLE dbo.Installment  
ADD SurchargeCalculated AS dbo.SurchargeCalc(days,Amount, XXXX) --where XXX should be InstPercenatage
GO

回答1:

Since you can't use a subquery directly on the computed column, you will need to do it on the scalar function itself :

CREATE FUNCTION SurchargeCal(@days as integer, @amount as money, @PlanKey as integer)
RETURNS decimal
AS
BEGIN
    DECLARE @result as decimal = 0;

    SELECT @result = @amount * @days * InstPercentage / 365 / 100
    FROM InstallMentPlan 
    WHERE PlanKey = @PlanKey    

    RETURN @result   
END

Now you can create the computed column, passing the PlanKey instead of its InstPercentage.

ALTER TABLE dbo.Installment  
ADD SurchargeCalculated AS dbo.SurchargeCalc(days, Amount, PlanKey)

来源：https://stackoverflow.com/questions/60264633/user-defined-scalar-function-to-generate-computed-column