Django: ORDER BY DESC on FloatField puts null values top?

问题

I'm surprised to find that an ORDER BY DESC query on a FloatField in Django returns null fields higher than fields with positive values.

# In models.py
class City(models.Model):
    name = models.CharField(max_length=30)
    country = models.ForeignKey(Country)
    value = models.FloatField(null=True, blank=True)
# In views.py
    cities = City.objects.filter(country__id=country.id).order_by('-value')
# In template.html
    {% for city in cities %}{{ city.name }}: {{ city.value }} --{% endfor %}

I get back the following:

  London: None -- Paris: None -- Berlin: 84.0 -- Tunis: 15.0 --

Instead, I want to return all the entries in descending order, with the None values last (i.e. Berlin, Tunis, London, Paris). Any way to do this?

回答1:

I think Django doesn't make any assumption about ordering of NULLs. Different SQL databases handle that ordering differently - SQLite/MySQL put NULLs at the top, Oracle at the bottom (for ascending ORDER BY clauses). So that's probably a problem with Django not "abstracting away" these differences.

But in most use cases, it doesn't make sense to include NULLs in sorted query results. If you really have a use case where you need it, you should probably sort manually (i.e. after making the query).

来源：https://stackoverflow.com/questions/4566939/django-order-by-desc-on-floatfield-puts-null-values-top