How to Efficiently Select Duplicate Values in Django Using ORM and SQL?

Selecting Duplicate Values in Django: An ORM and SQL Solution

In Django, if you have a model with non-unique fields that may have duplicate values, you may need to retrieve all rows with at least one duplicate value. This can be achieved using both the Django ORM and raw SQL.

Django ORM Solution:

To select rows with duplicate field values using the Django ORM, you can use the following approach:

from django.db.models import Count

dupes = Literal.objects.values('name')
                   .annotate(Count('id'))
                   .order_by()
                   .filter(id__count__gt=1)

This will return a ValuesQuerySet containing only the name field and a count of the id field. To obtain a regular QuerySet, you can use this as a subquery:

Literal.objects.filter(name__in=[item['name'] for item in dupes])

SQL Solution:

As an alternative to the Django ORM solution, you can also use raw SQL like this:

SELECT * FROM literal WHERE name IN (
    SELECT name FROM literal GROUP BY name HAVING COUNT((name)) > 1
);

Comparison and Performance Considerations:

The Django ORM solution is generally preferred as it is more concise and can leverage Django's optimization features. However, for complex queries or large datasets, the raw SQL solution may offer better performance.

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