Django数据库连接库问题

Question

我遇到了这种行为，不确定是否是错误。当我使用从创建的连接时cx_Oracle，它正在按假定的方式工作。但是，当我使用时Django DB connections，它给出的结果却不是预期的。

import cx_Oracle
from django.db import connections
import pandas as pd

dsn_tns = cx_Oracle.makedsn('xx.x.xx.xxx', 'port', 'dbname')
cx_Oracle_conn = cx_Oracle.connect('user', 'pass', dsn_tns)

django_conn = connections["DB2"] # In django settings, I have a created "DB2" and passed the same parameters.

query = ''' 
SELECT (T1.ACCEPTED- T2.CANCELLED) AS "NET" FROM
(
SELECT ID, COUNT(1) AS ACCEPTED FROM ACCEPTED_TABLE
GROUP BY ID
) T1
LEFT JOIN
(SELECT ID, COUNT(1) AS CANCELLED FROM CANCELLED_TABLE
GROUP BY ID) T2
ON T1.ID=T2.ID
'''

df1 = pd.read_sql(query, cx_Oracle_conn) # Gives right result
df2 = pd.read_sql(query, django_conn) # Gives only count of T1.ACCEPTED(T2.CANCELLED having 0 count)

问题：

1. 这是什么原因呢？连接如何影响查询的执行？
2. 这是Django的错误吗？还是我需要以其他方式使用Django连接？
3. 如何django.db.backends.oracle运作？能详细解释吗？

版本：

的Django == 2.1.2

Python == 3.6.7

'ENGINE': 'django.db.backends.oracle' # As mentioned in django document in DB connections