I have a .sql file which I'm trying to load in an online Python environment (JupyterHub) but other code I've found online has just left me confused. I've gotten as far as:
import sqlite3
from sqlite3 import connect
sqlite_uri = "sqlite:///basketball.db"
sqlite_engine = sqlalchemy.create_engine(sqlite_uri)
connection = sqlite3.connect(":memory:")
cursor = connection.cursor()
sql_file = open("travel-times.sql")
travel = sql_file.read()
travel
sql_expr = """
SELECT *
FROM travel;
"""
pd.read_sql(sql_expr, sqlite_engine)
and calling the 'travel' object does at least print the data in raw form, but from there I'm at a loss to actually load the table from here. What commands would accomplish this?
import sqlite3
conn = sqlite3.connect("test.db")
cursor = conn.cursor()
It should create the database, but it does not. Any help?
This code will create an sqlite db file called "test.db" in the same directory you are running your script from.
For example, if you have your python file in:
/home/user/python_code/mycode.py
And you run it from:
/home/user/
With:
python python_code/mycode.py # or python3
It will create an "empty" sqlite db file at
/home/user/test.db
If you can't find the test.db file, make sure you pass it the full path of where you want it to be located.
i.e.
conn = sqlite3.connect("/full/path/to/location/you/want/test.db")
I had the same problem, my .db file wasn't appearing because I forgot to add test.db at the end of path, see line 2 below
import sqlite3
databaseFile = "/home/user/test.db" #don't forget the test.db
conn = sqlite3.connect(databaseFile)
cursor = conn.cursor()
I suspect the DB will not be created on disk until you create at least one table in it. Just calling conn.cursor() is not sufficient.
Console sqlite3 utility behaves this way, too.
I am on windows 7 64 bit.
I have a csv file 'data.csv'.
I want to import data to a postgresql table 'temp_unicommerce_status' via a python script.
My Script is:
import psycopg2
conn = psycopg2.connect("host='localhost' port='5432' dbname='Ekodev' user='bn_openerp' password='fa05844d'")
cur = conn.cursor()
cur.execute("""truncate table "meta".temp_unicommerce_status;""")
cur.execute("""Copy temp_unicommerce_status from 'C:\Users\n\Desktop\data.csv';""")
conn.commit()
conn.close()
I am getting this error
Traceback (most recent call last):
File "C:\Users\n\Documents\NetBeansProjects\Unicommerce_Status_Update\src\unicommerce_status_update.py", line 5, in <module>
cur.execute("""Copy temp_unicommerce_status from 'C:\\Users\\n\\Desktop\\data.csv';""")
psycopg2.ProgrammingError: must be superuser to COPY to or from a file
HINT: Anyone can COPY to stdout or from stdin. psql's \copy command also works for anyone.
Use the copy_from cursor method
f = open(r'C:\Users\n\Desktop\data.csv', 'r')
cur.copy_from(f, temp_unicommerce_status, sep=',')
f.close()
The file must be passed as an object.
Since you are coping from a csv file it is necessary to specify the separator as the default is a tab character
The way I solved this problem particular to use psychopg2 cursor class function copy_expert (Docs: http://initd.org/psycopg/docs/cursor.html). copy_expert allows you to use STDIN therefore bypassing the need to issue a superuser privilege for the postgres user. Your access to the file then depends on the client (linux/windows/mac) user's access to the file
From Postgres COPY Docs (https://www.postgresql.org/docs/current/static/sql-copy.html):
Do not confuse COPY with the psql instruction \copy. \copy invokes
COPY FROM STDIN or COPY TO STDOUT, and then fetches/stores the data in
a file accessible to the psql client. Thus, file accessibility and
access rights depend on the client rather than the server when \copy
is used.
You can also leave the permissions set strictly for access to the development_user home folder and the App folder.
csv_file_name = '/home/user/some_file.csv'
sql = "COPY table_name FROM STDIN DELIMITER '|' CSV HEADER"
cursor.copy_expert(sql, open(csv_file_name, "r"))
#sample of code that worked for me
import psycopg2 #import the postgres library
#connect to the database
conn = psycopg2.connect(host='localhost',
dbname='database1',
user='postgres',
password='****',
port='****')
#create a cursor object
#cursor object is used to interact with the database
cur = conn.cursor()
#create table with same headers as csv file
cur.execute("CREATE TABLE IF NOT EXISTS test(**** text, **** float, **** float, ****
text)")
#open the csv file using python standard file I/O
#copy file into the table just created
with open('******.csv', 'r') as f:
next(f) # Skip the header row.
#f , <database name>, Comma-Seperated
cur.copy_from(f, '****', sep=',')
#Commit Changes
conn.commit()
#Close connection
conn.close()
f.close()
Here is an extract from relevant PostgreSQL documentation : COPY with a file name instructs the PostgreSQL server to directly read from or write to a file. The file must be accessible to the server and the name must be specified from the viewpoint of the server. When STDIN or STDOUT is specified, data is transmitted via the connection between the client and the server
That's the reason why the copy command to or from a file a restricted to a PostgreSQL superuser : the file must be present on server and is loaded directly by the server process.
You should instead use :
cur.copy_from(r'C:\Users\n\Desktop\data.csv', temp_unicommerce_status)
as suggested by this other answer, because internally it uses COPY from stdin.
You can use d6tstack which makes this simple
import d6tstack
import glob
c = d6tstack.combine_csv.CombinerCSV([r'C:\Users\n\Desktop\data.csv']) # single-file
c = d6tstack.combine_csv.CombinerCSV(glob.glob('*.csv')) # multi-file
c.to_psql_combine('postgresql+psycopg2://psqlusr:psqlpwdpsqlpwd#localhost/psqltest', 'tablename')
It also deals with data schema changes, create/append/replace table and allows you to preprocess data with pandas.
I know this question has been answered, but here are my two cent. I am adding little more description:
You can use cursor.copy_from method :
First you have to create a table with same no of columns as your csv file.
Example:
My csv looks like this:
Name, age , college , id_no , country , state , phone_no
demo_name 22 , bdsu , 1456 , demo_co , demo_da , 9894321_
First create a table:
import psycopg2
from psycopg2 import Error
connection = psycopg2.connect(user = "demo_user",
password = "demo_pass",
host = "127.0.0.1",
port = "5432",
database = "postgres")
cursor = connection.cursor()
create_table_query = '''CREATE TABLE data_set
(Name TEXT NOT NULL ,
age TEXT NOT NULL ,
college TEXT NOT NULL ,
id_no TEXT NOT NULL ,
country TEXT NOT NULL ,
state TEXT NOT NULL ,
phone_no TEXT NOT NULL);'''
cursor.execute(create_table_query)
connection.commit()
Now you can simply use cursor.copy_from where you need three parameters :
first file object , second table_name , third sep type
you can copy now :
f = open(r'final_data.csv', 'r')
cursor.copy_from(f, 'data_set', sep=',')
f.close()
done
I am going to post some of the errors I ran into trying to copy a csv file to a database on a linux based system....
here is an example csv file:
Name Age Height
bob 23 59
tom 56 67
You must install the library psycopg2 (i.e. pip install psycopg2 or sudo apt install python3-psycopg2 )
You must have postgres installed on your system before you can use psycopg2 (sudo apt install postgresql-server postgresql-contrib )
Now you must create a database to store the csv unless you already have postgres setup with a pre-existing database
COPY CSV USING POSTGRES COMMANDS
After installing postgres it creates a default user account which gives you access to postgres commands
To switch to the postgres account issue: sudo -u postgres psql
Acess the prompt by issuing: psql
#command to create a database
create database mytestdb;
#connect to the database to create a table
\connect mytestdb;
#create a table with same csv column names
create table test(name char(50), age char(50), height char(50));
#copy csv file to table
copy mytestdb 'path/to/csv' with csv header;
COPY CSV USING PYTHON
The main issue I ran into with copying the CSV file to a database was I didn't have the database created yet, however this can be done with python still.
import psycopg2 #import the Postgres library
#connect to the database
conn = psycopg2.connect(host='localhost',
dbname='mytestdb',
user='postgres',
password='')
#create a cursor object
#cursor object is used to interact with the database
cur = conn.cursor()
#create table with same headers as csv file
cur.execute('''create table test(name char(50), age char(50), height char(50));''')
#open the csv file using python standard file I/O
#copy file into the table just created
f = open('file.csv','r')
cursor.copy_from(f, 'test', sep=',')
f.close()
Try to do the same as the root user - postgres. If it were linux system, you could change file's permissions or move the file to /tmp. The problem results from missing credentials to read from the filesystem.
I am writing a very simply database using python and sqlite3. And when I created a table and some data I wanted to display this data using (in terminal) command "Select * From Data", but no data appears, although I checked using other methods that the data is inserted to the table.
How I create my table and data:
db = connect('database.db')
db_cursor = db.cursor()
db_cursor.execute("CREATE TABLE IF NOT EXISTS Data(Id INT, Name TEXT, City TEXT)")
db_cursor.execute("INSERT INTO Data VALUES (1, 'ABC', 'XYZ')")
If I do:
db_cursor.execute("Select * From Data")
print self.db_cursor.fetchall()
the data is displayed.
But when I run a command line and try to do:
sqlite3 database.db
sqlite> .mode column
sqlite> .headers on
sqlite> SELECT * FROM Data;
no data appears. I checked using
sqlite> .tables
that table is generated correctly.
Why sqlite3 run from command line does not display data?
You need to commit your transaction before it is permanently part of the database:
db.commit()
You can use the database connection as a context manager to commit automatically if a block of code executed successfully:
with db:
db_cursor = db.cursor()
db_cursor.execute("INSERT INTO Data VALUES (1, 'ABC', 'XYZ')")
Note that DDL statements (creating tables and other data definitions) are automatically committed, which is why you saw the table in the database, but not the new row.
I have been trying to create a sqlite database using one python file and access data from it using another, but keep getting an error. I have 2 files, main.py and file2.py
main.py:
import sqlite3, os
conn = sqlite3.connect(':memory:')
queryCurs = conn.cursor()
def createTable():
queryCurs.execute('''CREATE TABLE test(id INTEGER PRIMARY KEY, name TEXT)''')
def addInitial(name):
queryCurs.execute('''INSERT INTO test(name) VALUES (?)''',(name,))
createTable()
addInitial("John")
conn.commit()
os.system('file2.py')
and here is the code in file2.py
import sqlite3, os, time
conn = sqlite3.connect(':memory:')
queryCurs = conn.cursor()
queryCurs.execute('SELECT name FROM test WHERE id=1')
for i in queryCurs:
for j in i:
name = j
print name
conn.commit()
I receive the error: OperationalError: no such table: test
Each connect call creates its own in-memory database.
To share the same in-memory database, create a single connection and share that Python object in both modules.