A non-unique primary key allows the same value to be used for multiple records thus multiple results could be returned for Model.objects.get(pk=1).

A primary key is used to uniquely identify each record in the Model's database table.

primary_key=True denotes the field is the primary key for the model.

primary_key=True implies null=False and unique=True.

So in practice, do this

class SomeModel(models.Model):
    some_field = models.CharField(primary_key=True)

Instead of this

class SomeModel(models.Model):
    some_field = models.CharField(
        primary_key=True,
        unique=False
    )