MySQL and Python Select Statement Issues

Question

Thanks for taking the time to read this. It's going to be a long post to explain the problem. I haven't been able to find an answer in all the usual sources.

Problem: I am having an issue with using the select statement with python to recall data from a table in a mysql database.

System and versions:

Linux ubuntu 2.6.38-14-generic #58-Ubuntu SMP Tue Mar 27 20:04:55 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Python: 2.7.1+
MySql: Server version: 5.1.62-0ubuntu0.11.04.1 (Ubuntu)

Here's the table:

mysql> describe hashes;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | varchar(20)  | NO   | PRI | NULL    |       |
| hash  | varbinary(4) | NO   | MUL | NULL    |       |
+-------+--------------+------+-----+---------+-------+

Here are responses that I want via a normal mysql query:

mysql> SELECT id FROM hashes WHERE hash='f'; 
+------+
| id   |
+------+
| 0x67 |
+------+

mysql> SELECT id FROM hashes WHERE hash='ff'; 
+--------+
| id     |
+--------+
| 0x6700 |
+--------+

As before, these are the responses that are expected and how I designed the DB.

My code:

import mysql.connector
from database import login_info
import sys
db = mysql.connector.Connect(**login_info)
cursor = db.cursor()
data = 'ff'
cursor.execute("""SELECT
            * FROM hashes
            WHERE hash=%s""",
            (data))

rows = cursor.fetchall()
print rows
for row in rows:
        print row[0]

This returns the result I expect:

[(u'0x67', 'f')]
0x67

If I change data to : data = 'ff' I receive the following error:

Traceback (most recent call last):
 File "test.py", line 11, in <module>
    (data))
  File "/usr/local/lib/python2.7/dist-packages/mysql_connector_python-0.3.2_devel-    py2.7.egg/mysql/connector/cursor.py", line 310, in execute
    "Wrong number of arguments during string formatting")
mysql.connector.errors.ProgrammingError: Wrong number of arguments during string formatting

OK. So, I add a string formatting character to my SQL statement as so:

cursor.execute("""SELECT
            * FROM hashes
            WHERE hash=%s%s""",
            (data))

And I get the following response:

[(u'0x665aa6', "f'f")]
0x665aa6

and it should by 0x6700.

I know that I should be passing the data with one %s character. That is how I built my database table, using one %s per variable:

cursor.execute("""
INSERT INTO hashes (id, hash) 
VALUES (%s, %s)""", (k, hash))

Any ideas how to fix this?

Thanks.

Solution

Your execute statement doesn't seem quite correct. My understanding is that it should follow the pattern cursor.execute( <select statement string>, <tuple>) and by putting only a single value in the tuple location it is actually just a string. To make the second argument the correct data type you need to put a comma in there, so your statement would look like:

cursor.execute("""SELECT
            * FROM hashes
            WHERE hash=%s""",
            (data, ))