python 的引用错误 - 使用 pymssql

Question

我正在尝试使用 python 2.5.2 执行以下代码。该脚本正在建立连接并创建表，但随后失败并出现以下错误。

脚本

import pymssql
conn = pymssql.connect(host='10.103.8.75', user='mo', password='the_password', database='SR_WF_MODEL')
cur = conn.cursor()
cur.execute('CREATE TABLE persons(id INT, name VARCHAR(100))')
cur.executemany("INSERT INTO persons VALUES(%d, %s)", \
    [ (1, 'John Doe'), (2, 'Jane Doe') ])
conn.commit()

cur.execute("SELECT * FROM persons WHERE salesrep='%s'", 'John Doe')
row = cur.fetchone()
while row:
    print "ID=%d, Name=%s" % (row[0], row[1])
    row = cur.fetchone()

cur.execute("SELECT * FROM persons WHERE salesrep LIKE 'J%'")

conn.close()

错误有

Traceback (most recent call last):
  File "connect_to_mssql.py", line 9, in <module>
    cur.execute("SELECT * FROM persons WHERE salesrep='%s'", 'John Doe')
  File "/var/lib/python-support/python2.5/pymssql.py", line 126, in execute
    self.executemany(operation, (params,))
  File "/var/lib/python-support/python2.5/pymssql.py", line 152, in executemany
    raise DatabaseError, "internal error: %s" % self.__source.errmsg()
pymssql.DatabaseError: internal error: None

什么建议吗？另外，你如何阅读回溯错误，任何人都可以帮助我理解错误消息吗？你怎么读？自下而上？

Answer 1

我认为您假设常规的 python 字符串插值行为，即：

>>> a = "we should never do '%s' when working with dbs"
>>> a % 'this'
"we should never do 'this' when working with dbs"

execute 方法中的 % 运算符看起来像普通的字符串格式化运算符，但这更多的是一种方便或助记符；您的代码应为：

cur.execute("SELECT * FROM Persons WHERE salesrep=%s", 'John Doe')

不带引号，这适用于 O'Reilly 等名称，并提供帮助根据数据库适配器设计防止 SQL 注入。这就是数据库适配器的真正用途——将 python 对象转换为 sql；它会知道如何引用字符串并正确转义标点符号等。如果您这样做，它会起作用：

>>> THING_ONE_SHOULD_NEVER_DO = "select * from table where cond = '%s'"
>>> query = THING_ONE_SHOULD_NEVER_DO % 'john doe'
>>> query
"select * from table where cond = 'john doe'"
>>> cur.execute(query)

但这是不好的做法。