sql server - Dynamic SELECT does not work using @param in GROUP BY -

i'm trying following:

select   case               when @aggregation_zeit = 'day' day              when @aggregation_zeit = 'month' month              when @aggregation_zeit = 'year' year          end                                             time_field, ... group year,           case               when @aggregation_zeit = 'day' month               when @aggregation_zeit = 'month' month          end,          case               when @aggregation_zeit = 'day' day          end 

but keeps saying month , day invalid in select-list because not contained in aggregate function.

how can realize this?

thanks, felix

i'm assuming day, month, year numeric columns in table, if not let me know , i'll change answer.

select   case               when @aggregation_zeit = 'day' cast(datefromparts([year], [month], [day]) varchar(12))              when @aggregation_zeit = 'month' str([year]) + '/' + str([month])              when @aggregation_zeit = 'year' str([year])          end                                             time_field, ... group case               when @aggregation_zeit = 'day' cast(datefromparts([year], [month], [day]) varchar(12))              when @aggregation_zeit = 'month' str([year]) + '/' + str([month])              when @aggregation_zeit = 'year' str([year])          end