I have created a python program (with python3 and mysql.connector library) that updates the value of a column in a MySQL DB. When I run the command SELECT * FROM table_name in python seems to have changed the value, but when I run this command in MySql WorkBench it drops me the table with no changes applied.
Here is my code:
db = mysql.connector.connect(
host = "IP adress",
user = "user",
passwd = "password"
)
mycursor = db.cursor()
mycursor.execute("USE db_name;")
mycursor.execute('UPDATE table_name SET column = value WHERE condition;')
mycursor.execute('SELECT * FROM table_name;')
print(mycursor.fetchone())
As I have previously mentioned, when I run the command SELECT * FROM table_name in python it seems like the changes have been applied, but when I run it in MySql Workbench it seems like no changes have been applied. Does anybody know what the problem is?
try : before print(mycursor.fetchone())
db.commit()
Related
I want to connect to MySql database using Python through PythonAnywhere, without creating a Flask/Django application.
I have seemingly managed to connect through MySQLdb, using the code below, but I do not receive a response when I run the code. Any solutions?
import MySQLdb
db = MySQLdb.connect(
host = "myuser.mysql.pythonanywhere-services.com",
user = "myuser",
passwd = XXX,
db = "myuser$db_name"
)
cursor = db.cursor()
cursor.execute("SELECT * FROM table_name")
for x in cursor:
print(x)
cursor.close()
db.close()
You retrieve all rows in the table, without error.
cursor.execute("SELECT * FROM table_name")
for x in cursor:
print(x)
Yet you see no output. This is normal for a table that contains zero rows.
Consider doing one or more INSERTs, and a COMMIT,
prior to the query.
I'm trying to figure out why I can't access a particular table in a PostgreSQL database using psycopg2. I am running PostgreSQL 11.5
If I do this, I can connect to the database in question and read all the tables in it:
import psycopg2
try:
connection = psycopg2.connect(user = "postgres", #psycopg2.connect() creates connection to PostgreSQL database instance
password = "battlebot",
host = "127.0.0.1",
port = "5432",
database = "BRE_2019")
cursor = connection.cursor() #creates a cursor object which allows us to execute PostgreSQL commands through python source
#Print PostgreSQL version
cursor.execute("""SELECT table_name FROM information_schema.tables
WHERE table_schema = 'public'""")
for table in cursor.fetchall():
print(table)
The results look like this :
('geography_columns',)
('geometry_columns',)
('spatial_ref_sys',)
('raster_columns',)
('raster_overviews',)
('nc_avery_parcels_poly',)
('Zone5e',)
('AllResidential2019',)
#....etc....
The table I am interested in is the last one, 'AllResidential2019'
So I try to connect to it and print the contents by doing the following:
try:
connection = psycopg2.connect(user = "postgres",
#psycopg2.connect() creates connection to PostgreSQL database instance
password = "battlebot",
host = "127.0.0.1",
port = "5432",
database = "BRE_2019")
cursor = connection.cursor() #creates a cursor object which allows us to execute PostgreSQL commands through python source
cursor.execute("SELECT * FROM AllResidential2019;") #Executes a database operation or query. Execute method takes SQL query as a parameter. Returns list of result
record = cursor.fetchall()
print(record)
except (Exception, psycopg2.Error) as error:
print("Error while connecting to PostgreSQL: ", error)
And I get the following error:
Error while connecting to PostgreSQL: relation "allresidential2019" does not exist
LINE 1: SELECT * FROM AllResidential2019;
However, I can successfully connect and get results when attempting to connect to another table in another database I have (this works! and the results are the data in this table):
try:
connection = psycopg2.connect(user = "postgres", #psycopg2.connect() creates connection to PostgreSQL database instance
password = "battlebot",
host = "127.0.0.1",
port = "5432",
database = "ClimbingWeatherApp") . #different database name
cursor = connection.cursor()
cursor.execute("SELECT * FROM climbing_area_info ;")
record = cursor.fetchall()
print(record)
except (Exception, psycopg2.Error) as error:
print("Error while connecting to PostgreSQL: ", error)
I can't figure out why I can retrieve information from one table but not another, using exactly the same code (except names are changes). And I am also not sure how to troubleshoot this. Can anyone offer suggestions?
Your table name is case-sensitive and you have to close it in double quotes:
SELECT * FROM "AllResidential2019";
In Python program it may look like this:
cursor.execute('SELECT * FROM "AllResidential2019"')
or you can use the specialized module SQL string composition:
from psycopg2 import sql
# ...
cursor.execute(sql.SQL("SELECT * FROM {}").format(sql.Identifier('AllResidential2019')))
Note that case-sensitive Postgres identifiers (i.e. names of a table, column, view, function, etc) unnecessarily complicate simple matters. I would advise you not to use them.
Likely, the reason for your issue is Postgres' quoting rules which adheres to the ANSI SQL standard regarding double quoting identifiers. In your table creation, you likely quoted the table:
CREATE TABLE "AllResidential2019" (
...
)
Due to case sensitivity of at least one capital letter, this requires you to always quote the table when referencing the table. Do remember: single and double quotes have different meanings in SQL as opposed to being mostly interchangeable in Python.
SELECT * FROM "AllResidential2019"
DELETE FROM "AllResidential2019" ...
ALTER TABLE "AllResidential2019" ...
It is often recommended, if your table, column, or other identifier does not contain special characters, spaces, or reserved words, to always use lower case or no quotes:
CREATE TABLE "allresidential2019" (
...
)
CREATE TABLE AllResidential2019 (
...
)
Doing so, any combination of capital letters will work
SELECT * FROM ALLRESIDENTIAL2019
SELECT * FROM aLlrEsIdEnTiAl2019
SELECT * FROM "allresidential2019"
See further readings on the subject:
Omitting the double quote to do query on PostgreSQL
PostgreSQL naming conventions
Postgres Docs - 4.1.1. Identifiers and Key Words
Don’t use double quotes in PostgreSQL
What is the difference between single and double quotes in SQL?
I was facing the same error in Ubuntu. But in my case, I accidentally added the tables to the wrong database, which was in turn owned by the root postgres user instead of the new postgres user that I had created for my flask app.
I'm using a SQL file to create and populate the tables. This is the command that I used to be able to create these tables using a .sql file. This allows you to specify the owner of the tables as well as the database in which they should be created:
sudo -u postgres psql -U my_user -d my_database -f file.sql -h localhost
You will then be prompted for my_users's password.
sudo -u postgres is only necessary if you are running this from a terminal as a the root user. It basically runs the psql ... command as the postgres user.
I have looked at similar questions but nothing has worked for me so far
So here it is. I want to update my table through a python script. I'm using the module cx_oracle. I can execute a SELECT query but whenever I try to execute an UPDATE query, my program just hangs (freezes). I realize that I need to use cursor.commit() after cursor.execute() if I am updating a table but my code never gets past cursor.commit(). I have added a code snippet below that I am using to debug.
Any suggestions??
Code
import cx_Oracle
def getConnection():
ip = '127.0.0.1'
port = 1521
service_name = 'ORCLCDB.localdomain'
username = 'username'
password = 'password'
dsn = cx_Oracle.makedsn(ip, port, service_name=service_name) # (CONNECT_DATA=(SERVICE_NAME=ORCLCDB.localdomain)))
return cx_Oracle.connect(username, password, dsn) # connection
def debugging():
con = getConnection()
print(con)
cur = con.cursor()
print('Updating')
cur.execute('UPDATE EMPLOYEE SET LATITUDE = 53.540943 WHERE EMPLOYEEID = 1')
print('committing')
con.commit()
con.close()
print('done')
debugging()
**Here is the corresponding output: **
<cx_Oracle.Connection to username#(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=127.0.0.1)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=ORCLCDB.localdomain)))>
Updating
Solution
After a bit of poking around, I found the underlying cause! I had made changes to the table using Oracle SQL Developer but had not committed them, when the python script tried to make changes to the table it would freeze up because of this. To avoid the freeze, I committed my changes in oracle sql developer before running the python script and it worked fine!
Do you have any option to look in the database ? I mean , in order to understand whether is a problem of the python program or not, we need to check the v$session in the database to understand whether something is blocked.
select sid, event, last_call_et, status from v$session where sid = xxx
Where xxx is the sid of the session which has connected with python.
By the way, I would choose to commit explicitly after cursor execute
cur.execute('UPDATE EMPLOYEE SET LATITUDE = 53.540943 WHERE EMPLOYEEID = 1')
con.commit()
Hope it helps
Best
how do I create a database or table using python mysql connector where the name of the database/table has to be taken as a input from the user. I tried the following but it doesn't works:
mycursor.execute("create database %s", (database_name))
you should make connection without db name.
This should work
conn = pymysql.connect('localhost','user','password')
cur = conn.cursor(pymysql.cursors.DictCursor)
cur.execute('CREATE DATABASE %s;'%('DB_NAME_TO_MAKE'))
I am trying to create a database using pyodbc, however, I cannot find it seems to be paradox as the pyodbc needs to connect to a database first, and the new database is created within the linked one. Please correct me if I am wrong.
In my case, I used following code to create a new database
conn = pyodbc.connect("driver={SQL Server};server= serverName; database=databaseName; trusted_connection=true")
cursor = conn.cursor()
sqlcommand = """
CREATE DATABASE ['+ #IndexDBName +'] ON PRIMARY
( NAME = N'''+ #IndexDBName+''', FILENAME = N''' + #mdfFileName + ''' , SIZE = 4000KB , MAXSIZE = UNLIMITED, FILEGROWTH = 1024KB )
LOG ON
( NAME = N'''+ #IndexDBName+'_log'', FILENAME = N''' + #ldfFileName + ''' , SIZE = 1024KB , MAXSIZE = 100GB , FILEGROWTH = 10%)'
"""
cursor.execute(sqlcommand)
cursor.commit()
conn.commit()
The above code works without errors, however, there is no database created.
So how can I create a database using pyodbc?
Thanks a lot.
If you try to create a database with the default autocommit value for the connection, you should receive an error like the following. If you're not seeing this error message, try updating the SQL Server native client for a more descriptive message:
pyodbc.ProgrammingError: ('42000', '[42000] [Microsoft][SQL Server Native Client 11.0]
[SQL Server]CREATE DATABASE statement not allowed within multi-statement transaction.
(226) (SQLExecDirectW)')
Turn on autocommit for the connection to resolve:
conn = pyodbc.connect("driver={SQL Server};server=serverName; database=master; trusted_connection=true",
autocommit=True)
Note two things:
autocommit is not part of the connection string, it is a separate keyword passed to the connect function
specify the initial connection database context is the master system database
As an aside, you may want to check the #IndexDBName, #mdfFileName, and #ldfFileName are being appropriately set in your T-SQL. With the code you provided, a database named '+ #IndexDBName +' would be created.
The accepted answer did not work for me but I managed to create a database using the following code on Ubuntu:
conn_str = r"Driver={/opt/microsoft/msodbcsql17/lib64/libmsodbcsql-17.9.so.1.1};" + f"""
Server={server_ip};
UID=sa;
PWD=passwd;
"""
conn = pyodbc.connect(conn_str, autocommit=True)
cursor = conn.cursor()
cursor.execute(f"CREATE DATABASE {db_name}")
Which uses the default "master database" when connecting. You can check if the dataset is created by this query:
SELECT name FROM master.sys.databases