title: Django ORM query to get data from multiple tables
body: <p>I need to retrieve data from multiple tables to display shop name, shop location, shop monthly sales volume(unit), monthly sales amount, and sales person name who take orders from the shop.
  My sample table example below:</p>
  
  <p><strong>Order</strong></p>
  
  <pre><code>id      total_price   added_by_id(employee id)   customer_id
  1       42480         2                          1
  2       74920         3                          2
  3       21000         3                          2
  4       42480         2                          1
  </code></pre>
  
  <p><strong>OrderItem</strong></p>
  
  <pre><code>order_id      unit
  1             1
  1             2
  2             2
  2             2
  3             2
  4             5
  </code></pre>
  
  <p><strong>Customer</strong></p>
  
  <pre><code>id    full_name      location  
  1     Shop1          Example location1
  2     Shop2          Example location2
  </code></pre>
  
  <p><strong>Employee</strong></p>
  
  <pre><code>id    full_name      
  1     Employee Name1          
  2     Employee Name2          
  </code></pre>
  
  <p><strong>And the resultant table should be</strong></p>
  
  <pre><code>shop name    location     salesperson        sales volume   monthly sales
  Shop1        location1    Employee Name1     8              43630
  Shop2        location2    Employee Name2     6              95920
  </code></pre>
  
  <p><strong>My Try:</strong></p>
  
  <pre><code>Order.objects.select_related('account_customer').all()
  .values('customer_id')
  .annotate(total_sales=Sum('total_price'))
  .filter(created_at__year=today.year, created_at__month=today.month)
  </code></pre>
  
  <p>It will return</p>
  
  <pre><code>&lt;QuerySet [{'customer_id': 1, 'total_sales': Decimal('43630.00')}, {'customer_id': 2, 'total_sales': Decimal('95920.00')}]&gt;
  </code></pre>
  
  <p>I can't retrieve other necessary information like shop name, location, salesperson name sales volume.</p>
  
  <p>Related models:</p>
  
  <pre><code>class Order(models.Model):
      added_by = models.ForeignKey(Employee, on_delete=models.CASCADE)
      customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
      total_price = models.DecimalField(max_digits=18, decimal_places=2)
  
  class OrderItem(models.Model):
      order = models.ForeignKey(Order, on_delete=models.CASCADE)
      unit = models.FloatField()
  
  class Customer(models.Model):
      shop_name = models.CharField(max_length=100)
      address = models.CharField(max_length=100)
  
  class Employee(AbstractUser):
      full_name = models.CharField(max_length=100)
  </code></pre>
  
  <p>How can I retrieve all of my necessary information?</p>