I have written the below SP for Precheck for Duplicate records before insert into Table . but it is not allow me yo write insert staement inside the CASE .

how can I write Stored Procedure for fist Check the value @Ordername into table After that if it is not present then it should inserted into Database .

       CREATE PROCEDURE [Test Procedure ]
          (
          @section varchar(70), 
          @mark varchar(70),
          @qty decimal(18,2),
          @Weight decimal(18,2),
          @dateupdateremark int,
          @OrderName varchar(70)
           )
          AS
       BEGIN
   SET NOCOUNT ON;

       select case(@OrderName)
       when (select OrderName from dbo.tbl_insertxmldetails 
       where(@OrderName) not in (select OrderName from tbl_insertxmldetails))

       then 
       insert into dbo.tbl_insertxmldetails 
       (Section, Mark, QTY,Weight,Dateupdateremark ,OrderName,SystemDate)
       values
       (@Section, @Mark, @QTY,@Weight, @Dateupdateremark,@OrderName,GETDATE())
       else 'File already Exists'

end