SQL Query Advice

Question

Expert,
I have prepared the below query. Now I want to add constraint that the field OPCH.NumAtCard cannot have duplicate value please advice how can I enforce this condition. Is their any other option on how enforce it.
IF @transaction_type IN ( 'A' , 'U' ) AND @Object_type = '18'
BEGIN
IF EXISTS ( SELECT * FROM OPCH T0 WHERE T0.NumAtCard = ?? AND T0.DocType='I' AND T0.DOCENTRY = @list_of_cols_val_tab_del)
     BEGIN
          SELECT @Error = 2 , @error_message = 'A/R Invoice - Bill Already Entered'
     END
END
Faisal

Answer 1

Hi,
Try this
--Restrict Duplicate Vendor Reference Number in Purchase Invoice
if @object_type = '18'
and (@transaction_type = 'A' or @transaction_type = 'U')
begin
     declare @venno as varchar (100)
     declare @vennam as varchar (100)
     if (@object_type = '18')
     begin
          select @venno = NumAtCard, @vennam = CardCode from OPCH T0 where docentry = @list_of_cols_Val_tab_del
          begin
               if (@venno is not null)
               begin
                    if 1!= (select count (docentry) from OPCH with (nolock)where (NumatCard = @venno) and (cardcode = @vennam))
                    begin
                         select @error = 1
                         select @error_message = 'Duplicate Vendor Ref Number!'
                    End
               End
          End
     End
End
Regards,
Bala