gistfile1.txt

# PHP (theory, really - this is hundreds of lines of refacatoring)
jempe_users
  user_id
  blah
  blha
  blah

jempe_employees
  user_id
  blah
  blah
  blah

jempe_shoppers
  user_id
  blah
  blah
  blah

Jeff Bloo`m - Shopper, user_id = 6 

SELECT
  u.user_id

FROM
  jempe_users AS u

INNER JOIN
  jempe_employees
  AS e
    ON e.user_id = u.user_id

INNER JOIN
  jempe_shoppers
  AS s
    ON s.user_id = u.user_id

# Django (Same pattern, real code)
from django.contrib.auth.models import User

class Employee(User):
    employee_level = models.PositiveIntegerField()