if object_id('dbo.MyProcedure') is not null
    drop procedure dbo.MyProcedure;
--
-- MyProcedure: show how to use multiple parameters
--
create procedure MyProcedure(
    @pIn_ProductName nvarchar(100) = null,
    @pIn_StockUnit   nvarchar(100) = null,
    @pIn_ProductCode nvarchar(20) = null
)
as begin

    set nocount on;

    select ...
    from ...
    where
        (@pIn_ProductName is null or ProductName like @pIn_ProductName) and
        (@pIn_StockUnit is null or StockUnit like @pIn_StockUnit) and
        (@pIn_ProductCode is null or ProductCode like @pIn_ProductCode);

    return (0);
end; -- procedure