I am trying to fetch data from AWS MariaDB:
cursor = self._cnx.cursor()
stmt = ('SELECT * FROM flights')
cursor.execute(stmt)
print(cursor.rowcount)
# prints 2
for z in cursor:
print(z)
# Does not iterate
row = cursor.fetchone()
# row is None
rows = cursor.fetchall()
# throws 'No result set to fetch from.'
I can verify that table contains data using MySQL Workbench. Am I missing some step?
EDIT: re 2 answers:
res = cursor.execute(stmt)
# res is None
EDIT:
I created new Python project with a single file:
import mysql.connector
try:
cnx = mysql.connector.connect(
host='foobar.rds.amazonaws.com',
user='devuser',
password='devpasswd',
database='devdb'
)
cursor = cnx.cursor()
#cursor = cnx.cursor(buffered=True)
cursor.execute('SELECT * FROM flights')
print(cursor.rowcount)
rows = cursor.fetchall()
except Exception as exc:
print(exc)
If I run this code with simple cursor, fetchall raises "No result set to fetch from". If I run with buffered cursor, I can see that _rows property of cursor contains my data, but fetchall() returns empty array.
Your issue is that cursor.execute(stmt) returns an object with results and you're not storing that.
results = cursor.execute(stmt)
print(results.fetchone()) # Prints out and pops first row
For the future googlers with the same Problem I found a workaround which may help in some cases:
I didn't find the source of the problem but a solution which worked for me.
In my case .fetchone() also returned none whatever I did on my local(on my own Computer) Database. I tried the exact same code with the Database on our companies server and somehow it worked. So I copied the complete server Database onto my local Database (by using database dumps) just to get the server settings and afterwards I also could get data from my local SQL-Server with the code which didn't work before.
I am a SQL-newbie but maybe some crazy setting on my local SQL-Server prevented me from fetching data. Maybe some more experienced SQL-user knows this setting and can explain.
Related
I have an issue which is related to connection pool but I don't understand it.
Below is my code and this is the behavior:
Starting with empty table, I do SELECT query for non-existing value (no results)
Then I do INSERT query, it successfully inserts the value
HOWEVER, after inserting a new value, if I try to do more SELECT statements it only works 2 out of 3 times, always fails exactly every 3rd try (with pool size=3. ie with pool size=10 it will work exactly 9 out of 10 times)
finally, if i restart the script, with the initial SELECT commented out (but the value is in table before script ones) I get the inserted value and it works every time.
Why does this code seem to 'get stuck returning empty result for the connection that had no result' until restarting the script?
(note that it keep opening and closing connections from connection pool because this is taken from a web application where each connect/close is a different web request. Here i cut the whole 'web' aspect out of it)
#!/usr/bin/python
import mysql.connector
dbvars = {'host':'h','user':'u','passwd':'p','db':'d'}
# db has 1 empty table 'test' with one varchar field 'id'
con = mysql.connector.connect(pool_name="mypool", pool_size=3, pool_reset_session=False, **dbvars)
cur = con.cursor()
cur.execute("SELECT id FROM test WHERE id = '123';")
result = cur.fetchall()
cur.close()
con.close()
con = mysql.connector.connect(pool_name="mypool")
cur = con.cursor()
cur.execute("INSERT INTO test VALUES ('123');")
con.commit()
cur.close()
con.close()
for i in range(12):
con = mysql.connector.connect(pool_name="mypool")
cur = con.cursor()
cur.execute("SELECT id FROM test WHERE id = '123';")
result = cur.fetchall()
cur.close()
con.close()
print result
The output of the above is:
[(u'123',)]
[]
[(u'123',)]
[(u'123',)]
[]
[(u'123',)]
[(u'123',)]
[]
[(u'123',)]
[(u'123',)]
[]
[(u'123',)]
Again, if I don't do the initial SELECT before the insert, then all of them return 123 (if it's already in db). It seems the initial SELECT 'corrupts' one of the connections of the connection pool. Further, if I do 2 SELECTs for empty results before the INSERT, then 2 of the 3 connections are 'corrupt'. Finally if I do 3 SELECTs before the insert, it still works 1 of 3 times, because it seems the INSERT 'fixes' the connection (presumably by having 'results').
Ubuntu 18.04
Python 2.7.17 (released Oct 2019)
mysql-connector-python 8.0.21 (June 2020)
MySql server 5.6.10
It seems to be a rather severe bug in the python driver for MySQL. Perhaps some configuration incompatibility but clearly a bug as no error is shown yet it returns wrong query results.
I filed the bug report with MySQL team and it's status is currently 'verified'.
https://bugs.mysql.com/bug.php?id=102053
I am writing a script in python 3.x using mysqlconnector.
What I am trying to achieve right now is to check if there is a record inside my db which may be a duplicate to the one I am analyzing right now.
I came up with such code:
def fill_data(self, db_name, data):
cursor = self.cnx.cursor(buffered=True)
isDuplicate = cursor.execute(("SELECT destination FROM {0} WHERE destination = '{1}';")
.format(db_name, data['destination']))
print(cursor.statement)
self.commit()
print(isDuplicate is None)
Though I still get isDuplicate as None object. I tried to check via cursor.statement what statement is being passed to my db: it turned out that while in script I get None obj while passed in db that query works fine.
I also tried SELECT COUNT(1) FROM db_name which also gave me different results.
I am out of ideas: maybe you guys can help me out?
Update:
The solution that works for me was:
q = ("SELECT * FROM {0} WHERE destination = %s AND countryCode = %s AND prefix = %s")
.format(db_name)
cursor.execute(q, (data['destination'], data['country_code'], data['prefix']))
self.cnx.commit()
isDoubled = cursor.fetchone()
So at the end of the day it was all about fetching data from the cursor :)
Maybe the reason of your issue is the way you use execute() method.
Try to make some changes and see what is printed out:
def fill_data(self, db_name, data):
cursor = self.cnx.cursor(buffered=True)
q = 'SELECT count(*) FROM {} WHERE destination = %s'.format(db_name)
duplicate_count = cursor.execute(q, (data['destination'], )).fetchall()
print(duplicate_count)
Why should I provide query parameters this way? (article is on psql, but the core principles are the same as in mysql)
update
If you are still receiving "NoneType" object has no atribute "fetchall", then the error is probably here:
cursor = self.cnx.cursor(buffered=True)
Looks like you are not creating cursor at all. I can take a look at it if you post some code about cnx creation.
I have a Python application, in which I'm calling a MySQL stored procedure from my view, like so:
import mysql.connector
proc = 'audit_report'
parms = [data['schoolid'], dateToISO(data['startdatedefault'],'from'), dateToISO(data['enddatedefault'],'to'), joinIntList(data['studypgms'], joinWith), joinIntList(data['fedpgms'], joinWith), joinIntList(data['statuses'], joinWith), data['fullssndefault']]
conn = mysql.connector.connect(user='usr', database='db', password='pwd')
cursor = conn.cursor(dictionary=True)
cursor.callproc(proc, parms)
for result in cursor.stored_results():
print(result.fetchall())
I am getting the data returned as a list of tuples, the standard output. Since I'm using connector version 2.1.7, the docs say adding
dictionary=True
to the cursor declaration should cause the rowset to be returned as a list of dictionaries, with column name as the key of each dictionary. Main difference between my application and the example in the docs is that I'm using cursor.callproc(), whereas the examples use cursor.execute() with actual sql code.
I tried
print(cursor.column_names)
to see if I could get the column names that way, but all I get is
('#_audit_report_arg1', '#_audit_report_arg2', '#_audit_report_arg3', '#_audit_report_arg4', '#_audit_report_arg5', '#_audit_report_arg6', '#_audit_report_arg7')
which looks more like the input parameters to the stored procedure.
Is there any way to actually get the column names of the returned data? The procedure is somewhat complex and contains crosstab-type manipulation, but calling the same stored procedure from MySQL Workbench happily supplies the column names.
Normally, knowing what the output is supposed to be, I could hard-code column names, except this procedure crosstabs the data for the last few columns, and it is unpredictable what they will be until after the query runs.
Thanks...
You can use pymysql in python3 and it should work fine !!
import pymysql.cursors
connection = pymysql.connect(host='',
user='',
password='',
db='test',
charset='utf8mb4',
cursorclass=pymysql.cursors.DictCursor)
try:
with connection.cursor() as cursor:
# Read a single record
sql = "query"
cursor.execute(sql)
result = cursor.fetchone()
num_fields = len(cursor.description)
field_names = [i[0] for i in cursor.description]
print (field_names)
finally:
connection.close()
I am connecting to mysql database via mysql connector and running a simple query to pull a list of IDs. I need to loop over that list and pass them into some other code. For some reason I am getting a list of tuples. Is this expected behavior? If not, what am I doing wrong?
Here is the snippet of my code:
import mysql.connector
conn = mysql.connector.connect(host='127.0.0.1', database='t', user='r', password='pwd')
cursor = conn.cursor()
query = ( "select id from T where updated < '%s'" % (run_date) )
cursor.execute(query)
for row in cursor:
print (row)
cursor.close()
I am getting the following back (from an INT field in d/b):
(Decimal('991837'),)
(Decimal('991838'),)
(Decimal('991839'),)
(Decimal('991871'),)
(Decimal('991879'),)
(Decimal('991899'),)
(Decimal('992051'),)
(Decimal('992299'),)
(Decimal('992309'),)
if you want to access just the data in the row you need to go into the dictionary
first you must make it true in the cursor
cur = db.cursor( buffered=True , dictionary=True)
then the result will be like this :
{'Decimal' : '991837'}
i'm sure the Decimal is your row name
so when you need to access to the value do this
import mysql.connector
conn = mysql.connector.connect(host='127.0.0.1', database='t', user='r', password='pwd')
cursor = conn.cursor()
query = ( "select id from T where updated < '%s'" % (run_date) )
cursor.execute(query)
for row in cursor:
print (row['Decimal'])
cursor.close()
i hope it works for i was looking for this solution for the past 2 days and no answers
the only way i debugged i opened the debugger and print out all the variables
have fun with Python :)
Yes, this is expected behavior. Using the cursor as an iterable is basically equivalent to looping over it using the fetchone() method. From the documentation for fetchone() (emphasis mine):
This method retrieves the next row of a query result set and returns a
single sequence, or None if no more rows are available. By default,
the returned tuple consists of data returned by the MySQL server,
converted to Python objects. If the cursor is a raw cursor, no such
conversion occurs;
I am currently connecting to a Sybase 15.7 server using sybpydb. It seems to connect fine:
import sys
sys.path.append('/dba/sybase/ase/15.7/OCS-15_0/python/python26_64r/lib')
sys.path.append('/dba/sybase/ase/15.7/OCS-15_0/lib')
import sybpydb
conn = sybpydb.connect(user='usr', password='pass', servername='serv')
is working fine. Changing any of my connection details results in a connection error.
I then select a database:
curr = conn.cursor()
curr.execute('use db_1')
however, now when I try to run queries, it always returns None
print curr.execute('select * from table_1')
I have tried running the use and select queries in the same execute, I have tried including go commands after each, I have tried using curr.connection.commit() after each, all with no success. I have confirmed, using dbartisan and isql, that the same queries I am using return entries.
Why am I not getting results from my queries in python?
EDIT:
Just some additional info. In order to get the sybpydb import to work, I had to change two environment variables. I added the lib paths (the same ones that I added to sys.path) to $LD_LIBRARY_PATH, i.e.:
setenv LD_LIBRARY_PATH "$LD_LIBRARY_PATH":dba/sybase/ase/15.7/OCS-15_0/python/python26_64r/lib:/dba/sybase/ase/15.7/OCS-15_0/lib
and I had to change the SYBASE path from 12.5 to 15.7. All this was done in csh.
If I print conn.error(), after every curr.execute(), I get:
("Server message: number(5701) severity(10) state(2) line(0)\n\tChanged database context to 'master'.\n\n", 5701)
I completely understand where you might be confused by the documentation. Its doesn't seem to be on par with other db extensions (e.g. psycopg2).
When connecting with most standard db extensions you can specify a database. Then, when you want to get the data back from a SELECT query, you either use fetch (an ok way to do it) or the iterator (the more pythonic way to do it).
import sybpydb as sybase
conn = sybase.connect(user='usr', password='pass', servername='serv')
cur = conn.cursor()
cur.execute("use db_1")
cur.execute("SELECT * FROM table_1")
print "Query Returned %d row(s)" % cur.rowcount
for row in cur:
print row
# Alternate less-pythonic way to read query results
# for row in cur.fetchall():
# print row
Give that a try and let us know if it works.
Python 3.x working solution:
import sybpydb
try:
conn = sybpydb.connect(dsn="Servername=serv;Username=usr;Password=pass")
cur = conn.cursor()
cur.execute('select * from db_1..table_1')
# table header
header = tuple(col[0] for col in cur.description)
print('\t'.join(header))
print('-' * 60)
res = cur.fetchall()
for row in res:
line = '\t'.join(str(col) for col in row)
print(line)
cur.close()
conn.close()
except sybpydb.Error:
for err in cur.connection.messages:
print(f'Error {err[0]}, Value {err[1]}')