-groupby { values { "Day" { { groupby time_stamp } { orderby time_stamp,desc} } } }

The list is { groupby_name { { groupby column } { orderby column,order } } }

Add this to the query as any other filter with template::list::filter_where_clauses.

You can pass as many lists in to the values parameters of group by as columns you want to group on. If you add the listfilters tag to your ADP file, it will show the available grouping options as filters. Make sure you add groupby:optional in ad_page_contract.

Another trick is to hide the column when it is used to grouping. Just dynamically set the hide_p paramter for the list element that is in groupby.

^M = C-q C-m

Resulating in this sequence:

M-%
Query replace: C-q C-m with: C-q C-j