Django order_by вызывает LEFT JOIN

Может ли кто-нибудь сказать мне, почему, когда я добавляю order_by () , запрос, который получает вывод, изменяется с INNER JOIN на LEFT OUTER JOIN ?

Есть ли способ сохранить INNER JOIN -ness?

data = models.RetailSalesFact.objects.values('customer_key__customer_state', 
                                             'date_key__calendar_month_name')
data = data.filter(date_key__calendar_year=year)
data = data.annotate(sales=Sum('sales_quantity'))
data = data.order_by('date_key__calendar_month_name')

До:

SELECT Customer_Dimension.Customer_State, Date_Dimension.Calendar_Month_Name,
       SUM(Retail_Sales_Fact.Sales_Quantity) AS sales 
    FROM Retail_Sales_Fact  
    INNER JOIN Customer_Dimension 
        ON (Retail_Sales_Fact.Customer_Key = Customer_Dimension.Customer_Key) 
    INNER JOIN Date_Dimension 
        ON (Retail_Sales_Fact.Date_Key = Date_Dimension.Date_Key) 
    WHERE Date_Dimension.Calendar_Year = ?  
    GROUP BY Customer_Dimension.Customer_State, 
             Date_Dimension.Calendar_Month_Name 
    ORDER BY Date_Dimension.Calendar_Month_Name ASC

После:

SELECT Customer_Dimension.Customer_State, Date_Dimension.Calendar_Month_Name, 
       SUM(Retail_Sales_Fact.Sales_Quantity) AS sales 
    FROM Retail_Sales_Fact 
    INNER JOIN Customer_Dimension 
        ON (Retail_Sales_Fact.Customer_Key = Customer_Dimension.Customer_Key) 
    LEFT OUTER JOIN Date_Dimension 
        ON (Retail_Sales_Fact.Date_Key = Date_Dimension.Date_Key) 
    WHERE Date_Dimension.Calendar_Year = ?  
    GROUP BY Customer_Dimension.Customer_State, 
             Date_Dimension.Calendar_Month_Name 
    ORDER BY Date_Dimension.Calendar_Month_Name ASC