>>> from django.db import connection
>>> cursor = connection.cursor()
>>> cursor.execute("""
...  SELECT DISTINCT first_name
...  FROM people_person
...  WHERE last_name = %s""", ['Lennon'])
>>> row = cursor.fetchone()
>>> print row
['John']

from django.db import connection, models

class PersonManager(models.Manager):
  def first_names(self, last_name):
    cursor = connection.cursor()
    cursor.execute("""
      SELECT DISTINCT first_name
      FROM people_person
      WHERE last_name = %s""", [last_name])
    return [row[0] for row in cursor.fetchone()]

class Person(models.Model):
  first_name = models.CharField(max_length=50)
  last_name = models.CharField(max_length=50)
  objects = PersonManager()

>>> Person.objects.first_names('Lennon')
['John', 'Cynthia']