id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
32663	Remove Error raising on annotation & distinct call	Yovel Cohen	nobody	"if you try to call distinct on an annotated query, it sometimes works, sometimes get's ignore, and sometimes raises an error.
I had a query facing all three scenarios and solving the last one was the one that worked out.

the error being raised is:
```
NotImplementedError: annotate() + distinct(fields) is not implemented.
```
after looking at the source code for the exception at django.db.models.sql.compiler.SQLCompiler
row 594
```
if grouping:
        if distinct_fields:
           raise NotImplementedError('annotate() + distinct(fields) is not implemented.')
        order_by = order_by or self.connection.ops.force_no_ordering()
        result.append('GROUP BY %s' % ', '.join(grouping))
# rest of the as_sql() method
```

after just removing the distinct_fields condition:
```
if grouping:
        order_by = order_by or self.connection.ops.force_no_ordering()
        result.append('GROUP BY %s' % ', '.join(grouping))
# rest of the as_sql() method
```

it works, at least in the following ways I tried (annotations are just made up for sake of the example)
```
model_scores_latest_date_annotation = Max('model_scores__date')
latest_score_annotation = Case(When(model_scores__date=F('latest_date'), then='model_scores__score')
base_query_set = (Model.objects.filter(**filters).alias(latest_date=model_scores_latest_date_annotation).values(ID).annotate(latest_score=latest_score_annotation, latest_date=model_scores_latest_date_annotation)
```
adding the following distinct calls all worked:
```
query_set = base_query_set.order_by('latest_date').distinct('id', 'latest_date')

query_set = base_query_set.distinct('id')

query_set = base_query_set.distinct('id', 'latest_date')
```

which makes me think that the as_sql method on SQLCompiler can handle more cases easily and this just fell beneath the cracks.
"	Cleanup/optimization	new	Database layer (models, ORM)	3.2	Normal		SQLCompiler ORM Query		Unreviewed	0	0	0	0	0	0