Uniqueidentifier as parameter in SQL Server Function

Question

I have created a Function in SQL Server 2012 that I will use in a Check Constraint on a table. The function works as expected if I do:

SELECT [dbo].[CheckValidCardnumberForShellTankingen] ('700678036658047691' ,'2925CA00-6DD5-4F9D-AB0E-AA15DBBD388B')

But when I try to set the expression in Check Constraint so:

([dbo].[CheckValidCardnumberForShellTankingen]([Volledig kaartnummer],[RollBackCode])=(1))

I get a Messaage: "Error validating constraint 'CK_MyConstraint'"

I use the Uniqueidentifier in a Where clause and the strange thing is if I replace the parameter with string containing the Uniqueidentifier I dont get this error.

Here is the Function:

-- =============================================
-- Author:      Anders Pedersen
-- Create date: 2015-02-13
-- Description: Check of the Cardnumber of a transaction is valid.
-- =============================================
CREATE FUNCTION [dbo].[CheckValidCardnumberForShellTankingen]
(
    -- Add the parameters for the function here
    @Cardnumber NvarChar(50),
    @RollBackCode NvarChar(200)
)
RETURNS BIT
AS
BEGIN
    -- Declare the return variable here
    DECLARE 
     @Result                BIT
    ,@ResultLenght          BIT
    ,@ResultPrefix          BIT
    ,@CardLenght            INT
    ,@SupplierID            INT
    ,@UseCardnumber         BIT
    ,@Prefix                NvarChar(50)

    -- Add the T-SQL statements to compute the return value here
     SET @Result                = 0
     SET @ResultLenght          = 0
     SET @ResultPrefix          = 0
     SET @CardLenght            = -1
     SET @SupplierID            = -1
     SET @UseCardnumber         = 0
     SET @Prefix                = ''

    -- Get the UseCardnumber and the SupplierID
    SELECT @UseCardnumber = C.UseCardNumber, @SupplierID = F.SupplierID
    FROM Client C INNER JOIN
        ClientFileUploads F ON C.ClientID = F.ClientID
    WHERE F.RollBackCode = @RollBackCode
    --WHERE F.RollBackCode = '2925CA00-6DD5-4F9D-AB0E-AA15DBBD388B' 

    -- Only carry out the check if the Client use Cards else set the check to True (1)
    IF @UseCardnumber = 1
    BEGIN
        SELECT  @CardLenght =  [CardNumberLenght], @Prefix = ISNULL([Prefix],'') FROM [dbo].[Supplier] AS S WHERE S.SupplierID = @SupplierID

        IF (@CardLenght IS NULL) OR (@CardLenght = 0)
        BEGIN
            SET @ResultLenght = 1
        END
        ELSE
        BEGIN
        IF  (LEN(@Cardnumber) - @CardLenght)= 0
            BEGIN
                SET @ResultLenght = 1
            END
            ELSE
            BEGIN
                SET @ResultLenght =  0
            END
        END

        IF  SUBSTRING(@Cardnumber, 1, LEN(@Prefix)) = @Prefix
        BEGIN
            SET @ResultPrefix = 1
        END
        ELSE
        BEGIN
            SET @ResultPrefix =  0
        END

        IF ((@ResultLenght = 1) AND (@ResultPrefix = 1))
        BEGIN
            SET @Result = 1
        END
        ELSE
        BEGIN
            SET @Result = 0
        END     
    END
    ELSE
    BEGIN
        SET @Result = 1
    END

    -- Return the result of the function
    RETURN @Result

END

GO

Answer 1

If @RollBackCode is a uniqueidentifier, I recommend making the parameter a uniqueidentifier and not a varchar.

As Rhys Jones points out, you shouldn't use a UDF in a check constraint.

See
https://dba.stackexchange.com/questions/22297/udf-in-check-constraint-downside

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/078b720f-faac-425c-b51a-33bcecb263d2/check-constraint-with-udf-problem-with-lots-of-data?forum=transactsql

http://sqlblog.com/blogs/tibor_karaszi/archive/2009/12/17/be-careful-with-constraints-calling-udfs.aspx

If you need to check in a trigger and roll back -- SQL Server - After Insert/ For Insert - Rollback