SQL examples from Django's "defer" test app (since it lacks MQL tests, this bug went undetected):

>>> Primary.objects.defer("name")

SELECT "defer_primary"."id", "defer_primary"."value", "defer_primary"."related_id" FROM "defer_primary

>>> Primary.objects.only("only")

SELECT "defer_primary"."id", "defer_primary"."name" FROM "defer_primary

On MongoDB, the queries don't include the necessary $project to limit the keys returned: db.defer_primary.aggregate([\{'$limit': 1}])

Probably logic in SQLCompiler.columns is at fault. Query.get_select_mask() is where the deferred columns are computed.