title: How to apply a query on 2 databases (having no foreign keys) in Django?
body: <p>File <code>myapp/models.py</code> has this sample code..</p>
  
  <pre><code>from django.db import models
  
  # model for 'user' table in database oracle_dbuser1:user 
  class User(models.Model):
      . . .
      customerid = models.BigIntegerField()
  
  # model for 'customer' table in database oracle_dbuser2:customer
  # Note that there is no Foreign key integrity among these legacy tables.
  class Customer(models.Model):
      . . .
      customerid = models.BigIntegerField()
  </code></pre>
  
  <p>and the file <code>myapp/admin.py</code> has the following code:</p>
  
  <pre><code>from maasusers.models import User, Customer
  from django.contrib import admin
  
  class UserAdmin(admin.ModelAdmin):
      # A handy constant for the name of the alternate database.
      db_one = 'dbuser1'
      db_two = 'dbuser2'
  
      # display in a list
      list_display = (. . .) # question 1
  
      def queryset(self, request):
          result = super(UserAdmin, self).queryset(request).using(self.db_one) # question 2
          return result
  
  # Register the Poll class
  admin.site.register(User, UserAdmin)
  admin.site.register(Customer, UserAdmin)
  </code></pre>
  
  <p>Question 1: Refer above: I want to display columns of both the tables. How can I achieve this? Eg. <code>Select usr.col1, usr.col2, cust.col1, cust.col10 from user usr, customer cust where usr.col2 = cust.col3;</code></p>
  
  <p>Question 2: How to write a corresponding <code>queryset()</code> function using the <code>using</code> function?</p>