Retrieving data returns none - python

I am trying to retrieve all rows in mysql.
import mysql.connector,sys
user,pw, host,db = 'root','12345','127.0.0.1','CA2Database'
cnx = mysql.connector.connect(user=user, password=pw, host=host, database=db)
cursor = cnx.cursor()
try:
print(cursor.execute('SELECT * FROM student'))
except mysql.connector.Error as err:
print(err)
print("Error Code:", err.errno)
print("SQLSTATE", err.sqlstate)
print("Message", err.msg)
finally:
print()
The output is None . There is data in the table.
https://imgur.com/a/APUuZot

Probably you were missing some necessary function calls. This should do:
user,pw, host,db = 'root','12345','127.0.0.1','CA2Database'
cnx = mysql.connector.connect(user=user, password=pw, host=host, database=db)
cursor = cnx.cursor()
sql_query = 'SELECT * FROM student;'
cursor.execute(sql_query)
data = cursor.fetchall()
cnx.commit()
cursor.close()

Related

Python: MySQL is not updating record despite of using Commit

I am facing a weird issue. I have the following code. The INSERTS go well but the update query does not work at all. The rowcount is also shown 1 still when I check in Table Plus it does not reflect.
When I directly run the query UPDATE shop_links set product_status = 3 where shop_url = 'https://example.com' in TablePlus it does show record.
The irony is, the update query which set to 1 works just fine and updates instantly
import mysql.connector
def get_connection(host, user, password, db_name):
connection = None
try:
# connection = pymysql.connect(host=host,
# user=user,
# password=password,
# db=db_name,
# charset='utf8',
# max_allowed_packet=1073741824,
# cursorclass=pymysql.cursors.DictCursor)
connection = mysql.connector.connect(
host=host,
user=user,
use_unicode=True,
password=password,
database=db_name
)
connection.set_charset_collation('utf8')
print('Connected')
except Exception as ex:
print(str(ex))
finally:
return connection
with connection.cursor() as cursor:
sql = 'INSERT INTO {} (shop_url,product_url) VALUES (%s, %s)'.format(TABLE_FETCH_PRODUCTS)
cursor.executemany(sql, records)
connection.commit()
with connection.cursor() as cursor:
# Update the shop URL
# sql = "UPDATE {} set product_status = 3 where shop_url = '{}' ".format(TABLE_FETCH, shop_url)
sql = "UPDATE {} set product_status = 3 where shop_url = %s ".format(TABLE_FETCH, shop_url)
print(sql)
print('----------------------------------------------------------------')
cursor.execute(sql, (shop_url,))
connection.commit()

Python and PostGres | Showing data in a QLabel (psycopg2)

im using Postgres together with python(psycopg2). Im trying to insert data in a QLabel. It shows the data, but the data comes with clinges. How do I get rid of the clinges?
My code:
def getstunden():
conn = None
try:
conn = psycopg2.connect("dbname=test user=postgres password=test")
cur = conn.cursor()
cur.execute("SELECT stunden FROM ueberstunden WHERE name = 'test'")
row = cur.fetchone()
while row is not None:
self.s_test.setText(str(row))
row = cur.fetchone()
cur.close()
except (Exception, psycopg2.DatabaseError) as error:
print(error)
finally:
if conn is not None:
conn.close()
This is what I get out of it:
I want it to just show 12
Per here Cursor:
Note
cursor objects are iterable, so, instead of calling explicitly fetchone() in a loop, the object itself can be used:
cur.execute("SELECT * FROM test;")
for record in cur:
print record
(1, 100, "abc'def")
(2, None, 'dada')
(3, 42, 'bar')
So to simplify:
def getstunden():
conn = None
try:
conn = psycopg2.connect("dbname=test user=postgres password=test")
cur = conn.cursor()
cur.execute("SELECT stunden FROM ueberstunden WHERE name = 'test'")
for row in cur:
self.s_test.setText(str(row[0]))
cur.close()
except (Exception, psycopg2.DatabaseError) as error:
print(error)
finally:
if conn is not None:
conn.close()
It's just like this
print(row[0])
in your code
def getstunden():
conn = None
try:
conn = psycopg2.connect("dbname=test user=postgres password=test")
cur = conn.cursor()
cur.execute("SELECT stunden FROM ueberstunden WHERE name = 'test'")
row = cur.fetchone()
while row is not None:
#row without the brackets
self.s_test.setText(str(row[0]))
row = cur.fetchone()
cur.close()
except (Exception, psycopg2.DatabaseError) as error:
print(error)
finally:
if conn is not None:
conn.close()

how to overwrite or skip data when the same data is already existed in database?

i'm taking data from textfile which contains some duplicate data.And i'm trying to insert them into database without duplicating.i'm in trouble where inserting duplicate data.it should not be inserted again.data are not static values.
text_file = open(min_file, "r")
#doc = text_file.readlines()
for line in text_file:
field = line.split(";")
print(field)
try:
connection = mysql.connector.connect(host='localhost',
database='testing',
user='root',
password='root')
if connection.is_connected():
db_Info = connection.get_server_info()
print("Connected to MySQL Server version ", db_Info)
cursor = connection.cursor()
cursor.execute("select database();")
record = cursor.fetchone()
print("You're connected to database: ", record)
mycursor = connection.cursor()
#before inserting
mycursor.execute("Select * from ftp")
myresult = mycursor.fetchall()
for i in myresult:
print(i)
sql ="Insert into ftp(a,b,c,d) \
select * from( Select VALUES(%s,%s,%s,%s) as temp \
where not exists \
(Select a from ftp where a = %s) LIMIT 1"
mycursor.execute(sql,field)
print(mycursor.rowcount, "record inserted.")
connection.commit()
except Error as e:
print("Error while connecting to MySQL", e)
finally:
if connection.is_connected():
cursor.close()
connection.close()
print("MySQL connection is closed")
One option is to add Unique constraint and let the DB validate uniqueness, this will throw exception which you can catch and skip.

How to use python to query database in parallel

I have two functions which I use to query database. Assuming two separate queries, how to run these in parallel to query same database, and also wait for both results to return before continuing the execution of the rest of the code?
def query1(param1, param2):
result = None
logging.info("Connecting to database...")
try:
conn = connect(host=host, port=port, database=db)
curs = conn.cursor()
curs.execute(query)
result = curs
curs.close()
conn.close()
except Exception as e:
logging.error("Unable to access database %s" % str(e))
return result
def query2(param1, param2):
result = None
logging.info("Connecting to database...")
try:
conn = connect(host=host, port=port, database=db)
curs = conn.cursor()
curs.execute(query)
result = curs
curs.close()
conn.close()
except Exception as e:
logging.error("Unable to access database %s" % str(e))
return result
Here is a multi-threaded code that does what you're trying to accomplish:
from threading import Thread, Lock
class DatabaseWorker(Thread):
__lock = Lock()
def __init__(self, db, query, result_queue):
Thread.__init__(self)
self.db = db
self.query = query
self.result_queue = result_queue
def run(self):
result = None
logging.info("Connecting to database...")
try:
conn = connect(host=host, port=port, database=self.db)
curs = conn.cursor()
curs.execute(self.query)
result = curs
curs.close()
conn.close()
except Exception as e:
logging.error("Unable to access database %s" % str(e))
self.result_queue.append(result)
delay = 1
result_queue = []
worker1 = DatabaseWorker("db1", "select something from sometable",
result_queue)
worker2 = DatabaseWorker("db1", "select something from othertable",
result_queue)
worker1.start()
worker2.start()
# Wait for the job to be done
while len(result_queue) < 2:
sleep(delay)
job_done = True
worker1.join()
worker2.join()

How to use "INSERT" in psycopg2 connection pooling?

I use psycopg2 to connect to PostgreSQL on Python and I want to use connection pooling.
I don't know what should I do instead commit() and rollback() when I execute INSERT query.
db = pool.SimpleConnectionPool(1, 10,host=conf_hostname,database=conf_dbname,user=conf_dbuser,password=conf_dbpass,port=conf_dbport)
# Get Cursor
#contextmanager
def get_cursor():
con = db.getconn()
try:
yield con.cursor()
finally:
db.putconn(con)
with get_cursor() as cursor:
cursor.execute("INSERT INTO table (fields) VALUES (values) RETURNING id")
id = cursor.fetchone()
I don't get id of inserted record without commit().
UPDATE I can not test the code but I give you some ideas:
You do the commit in connection not in db
# Get Cursor
#contextmanager
def get_cursor():
con = db.getconn()
try:
yield con
finally:
db.putconn(con)
with get_cursor() as cursor:
con.cursor.execute("INSERT INTO table (fields) VALUES (values) RETURNING id")
con.commit()
id = cursor.fetchone()
or
# Get Cursor
#contextmanager
def get_cursor():
con = db.getconn()
try:
yield con.cursor()
con.commit()
finally:
db.putconn(con)
with get_cursor() as cursor:
con.cursor.execute("INSERT INTO table (fields) VALUES (values) RETURNING id")
id = cursor.fetchone()
Connection pooling exist because creating a new connection to a db can be expensive and not to avoid commits or rollbacks. So you can commit your data without any issue, committing data will not destroy the connection.
here is my working example:
db = pool.SimpleConnectionPool(1, 10,host=conf_hostname,database=conf_dbname,user=conf_dbuser,password=conf_dbpass,port=conf_dbport)
#contextmanager
def get_connection():
con = db.getconn()
try:
yield con
finally:
db.putconn(con)
def write_to_db():
with get_connection() as conn:
try:
cursor = conn.cursor()
cursor.execute("INSERT INTO table (fields) VALUES (values) RETURNING id")
id = cursor.fetchone()
cursor.close()
conn.commit()
except:
conn.rollback()
I think this will be a little more pythonic:
db_pool = pool.SimpleConnectionPool(1, 10,
host=CONF.db_host,
database=CONF.db_name,
user=CONF.db_user,
password=CONF.db_user,
port=CONF.db_port)
#contextmanager
def db():
con = db_pool.getconn()
cur = con.cursor()
try:
yield con, cur
finally:
cur.close()
db_pool.putconn(con)
if __name__ == '__main__':
with db() as (connection, cursor):
try:
cursor.execute("""INSERT INTO table (fields)
VALUES (values) RETURNING id""")
my_id = cursor.fetchone()
rowcount = cursor.rowcount
if rowcount == 1:
connection.commit()
else:
connection.rollback()
except psycopg2.Error as error:
print('Database error:', error)
except Exception as ex:
print('General error:', ex)

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