Extra select fields are merged into 'GROUP BY'

[Gregory]

Fields are merged into 'GROUP BY', when using some extra select fields and query.group_by attribute.

        fragments = Fragment.objects.all().extra(
            select = {'au_names': 'GROUP_CONCAT(lib_author.surnames ORDER BY names DESC SEPARATOR ", ")'},
        )
        fragments.query.group_by = ['lib_fragment.id']
        fragments.query.join((None, 'lib_fragment', None, None))

        connection = (
            'lib_fragment',
            'lib_fragment_authors',
            'id',
            'fragment_id',
        )
        fragments.query.join(connection, promote=True)

        connection = (
            'lib_fragment_authors',
            'lib_author',
            'author_id',
            'id',
        )
        fragments.query.join(connection, promote=True)

SELECT
    (GROUP_CONCAT(lib_author.surnames ORDER BY names DESC SEPARATOR ", ")) AS `au_ids`, 
FROM `lib_fragment` 
    LEFT OUTER JOIN `lib_fragment_authors` ON (`lib_fragment`.`id` = `lib_fragment_authors`.`fragment_id`) 
    LEFT OUTER JOIN `lib_author` ON (`lib_fragment_authors`.`author_id` = `lib_author`.`id`) 
GROUP BY (lib_fragment.id), (GROUP_CONCAT(lib_author.surnames ORDER BY names DESC SEPARATOR ", ")) 
ORDER BY `lib_fragment`.`id`

[Russell Keith-Magee]

qs.query.group_by (in fact, the entire qs.query structure) is an internal implementation detail. It isn't designed to be modified by end users. We don't (and won't) make any guarantees about how qs.query.group_by interacts with any other part of a query. We don't even guarantee that it will continue to exist.