cx_oracle 缺少右括号

Question

我正在使用 cx_oracle python 库来查找在过去 90 分钟内具有 modifiedDate 的任何记录。

import cx_Oracle

import datetime

from datetime import timedelta

import config as config

timeNow = datetime.datetime.now()

previousTime = timeNow - datetime.timedelta (minutes = 0)

connection = cx_Oracle.connect(user, password, connection)

cur = connection.cursor()

statement = "SELECT * FROM woodburn_all WHERE modifiedDate >= to_date(" + str(previousTime) +")"

print statement

r = cur.execute(statement)

for row in cur:

    print row

打印的 select 语句看起来正确：

SELECT * FROM woodburn_all WHERE to_date(modifiedDate) >= to_date(2018-09-2 11:02:10.460000)

我没有看到我错过了什么括号。这是一些奇怪的日期/时间吗？