It is possible to group by on multiple attribute values with the native API and SphinxQL but not with the Storage Engine.

The patch implements a new mode ("multi:") for the groupby function SPH_GROUPBY_MULTIPLE.

After the patch it is possible to group by on multiple attribute values with this query:

SELECT _sph_count, attribute1, attribute2 FROM sphinx_index_table WHERE query = ';groupby=multi:attribute1, attribute2';