Question

I generating a string for my Primarykey column similar identity function. but its behavior is unexpected.
it Removing all 0 by String and storing only a single character. Correct me Where am i wrong..

Alter FUNCTION [dbo].[UDF_GenerateBatchNumber]  (@BatchNumber as Varchar(10))
Returns Varchar
AS
BEGIN
    -- Declare the return variable here

    -- Add the T-SQL statements to compute the return value here
    Select Top(1) @BatchNumber=[BatchNo] From TBL_iBATCH Order by [BatchNo] desc
    IF @BatchNumber is Null
        BEGIN
         Set @BatchNumber ='B000001'
        END
    Else
        BEGIN
          Set @BatchNumber='B'+Convert(Varchar(7),(Cast(SUBSTRING(@BatchNumber,2,7) as Integer)+1))
        END  

    RETURN @BatchNumber

END

Answer 1

The usual way is to have a computed column using your IDENTITY column.

This UDF will fail under load and give 2 keys the same

ALTER  TABLE TBL_iBATCH
   ADD BatchNumber AS CAST('B' + RIGHT('000000' + CAST(MyIDCol AS varchar(6)), 6) AS char(7)) PERSISTED;

ALTER  TABLE TBL_iBATCHWITH CHECK 
   ADD CONSTRAINT PK_TBL_iBATCH PRIMARY KEY (BatchNumber);