create procedure [dbo].[sp_Sum]
(
@var nvarchar(50)
)
as
begin
declare @sql varchar(4000)
select @sql = 'select sum(' + @var + ') from table'
exec (@sql)
end

create procedure [dbo].[sp_Sum]
(
	@col nvarchar(50),
	@tbl nvarchar(50)
)

as

      declare     @iCntCol int,
                  @iCntTbl int,
                  @sql nvarchar(300)


      set @col = 'myCol'
      set @tbl = 'myTbl'

      select @iCntTbl = count(table_name) from
      information_schema.tables where table_name = @tbl

      if @iCntTbl = 1
            begin
                  select @iCntCol = count(column_name) from
                  information_schema.columns where table_name = @tbl 
                  and column_name = @col

                  if @iCntCol = 1
                        begin
                              select @sql = 'select sum(' + @col + ') from ' + @tbl
                              exec (@sql)
                        end
            end

select sum(case @col when 'col1' then col 
                     when 'col2' then col2
                     when 'col9' then col9
                     end)
from   table