Search for name in cx_Oracle

问题:

I have var='smth' and I need to check if var exists in the table 'smtb'

I tried something this, but it does not work:

rows=curs.fetchall()
for row in rows:
            if var==row:
                print("Yes")

When I print elements of rows, I get some pattern like this:

('element',)

How can I check whether var exists in the table?

回答1:

Don't do this in Python. If you want to search for something in a database table by far the quickest and most efficient way is to do it in SQL. Don't forget to use bind variables.

Assuming you have a cursor object curs it might look something like this (assuming your table is unique on var).

>>> sql = "select * from my_table where var = :var"
>>> bind_variables = {'var' : 'smth'}
>>>
>>> curs.execute(sql, bind_variables)
[<cx_Oracle.STRING with value None>]
>>> results = curs.fetchall()
>>> results
[('smth',)]
>>> try:
...     var = results[0][0]
...     print ('Yes')
... except IndexError:
...     print ('No')
...
Yes

Then if you're looking for something that doesn't exist you get the following.

>>> bind_variables = {'var' : 'other'}
>>> results = curs.fetchall()
>>> results
[]
>>> try:
...     var = results[0][0]
...     print ('Yes')
... except IndexError:
...     print ('No')
...
No

The actual reason why you don't get what you expect is that cx_Oracle returns a list of tuples as per PEP 249. You're expecting only one column to be returned so you need an access the 0^th index of the tuple, if you want to do it in the manner you are.

>>> rows = [('other',),('smth',)]
>>> var = 'smth'
>>> for row in rows:
...     if var == row[0]:
...         print ('Yes')
...
Yes