Question

我的查询：

SELECT * 
FROM employee.emp_details 
WHERE id = 7

这是我的代码

from cassandra.cluster import Cluster

HOST = ['10.107.2.123']
PORT = '9042'
cluster = Cluster(HOST, PORT)
session = cluster.connect()

val = 'FROM'
rows = session.execute('''SELECT * %s employee.emp_details WHERE id = %s''', (val, 7))

这是我得到的错误：

追踪（最近的呼叫最后）：
  文件＆＃34; /home/sachhya/Documents/Example/ex.py" ;,第9行，中
  rows = session.execute（＆＃39;＆＃39;＆＃39; SELECT *％s employee.emp_details WHERE id =％s＆＃39;＆＃39;＆＃39;，（val，7））
  文件＆＃34; /usr/local/lib/python3.6/dist-packages/cassandra/cluster.py" ;,第2134行，执行中
  return self.execute_async（query，parameters，trace，custom_payload，timeout，execution_profile，paging_state）.result（）
  文件＆＃34; /usr/local/lib/python3.6/dist-packages/cassandra/cluster.py" ;,第4026行，结果
  提升self._final_exception
  cassandra.protocol.SyntaxException：

我相信我的查询字符串是在参数绑定之后做出的。 SELECT * 'FROM' employee.emp_details WHERE id = 7

请帮助我使用＆＃39; val＆＃39;要在我的查询字符串中绑定的变量。

Answer 1

从技术上讲，您不必在查询中绑定FROM。在这种情况下使用字符串格式：

rows = session.execute('''SELECT * {} employee.emp_details WHERE id = %s'''.format(val), (7,))

Answer 2

from cassandra.cluster import Cluster

HOST = ['10.107.2.123']
PORT = '9042'
cluster = Cluster(HOST, PORT)
session = cluster.connect()

val = 'FROM'
query = 'SELECT * {} employee.emp_details WHERE id = {}'.format(val, 7)

# or query = ('SELECT * %s employee.emp_details WHERE id = %s' % (a, 7))

rows = session.execute(query)

来自终端的输出：

>>> query = ('SELECT * %s employee.emp_details WHERE id = %s' % (a, 7))
>>> query
'SELECT * FROM employee.emp_details WHERE id = 7'

>>> query = 'SELECT * {} employee.emp_details WHERE id = {}'.format(a, 7)
>>> query
'SELECT * FROM employee.emp_details WHERE id = 7'

Answer 3

让我告诉你预备陈述的力量。

from cassandra.cluster import Cluster

HOST = ['10.107.2.123'] PORT = '9042' cluster = Cluster(HOST, PORT) session = cluster.connect()

val=7

query="SELECT * employee.emp_details WHERE id = ?" prepared_query=session.prepare(prepared_query)

results=session.execute(prepared_query,(val))

print results

在必须迭代查询中的变量时使用预备语句。

访问：Prepared Statements Docs

如何在.execute方法

3 个答案: