I have a several postgres and mysql cursor objects exposed to me, created in some universe. How to find the database name (and other info about that db) from these cursor objects?
cursor.__dict__ gives nothing useful.
If you also have the connection (call it conn):
conn.info.dbname
I don't know about postgres but using MySQLdb you could always use the following:
cursor.execute("select database()")
db_name = cursor.fetchone()[0]
Maybe there's a cleaner way to do this...
Edit:
for other info it depends on what exactly you're looking for but for example to fetch table names
cursor.execute("show tables")
for r in cursor.fetchall():
print r[0]
There are many other functions available... Is there anything specific you're looking for?
for postgresql:-
cursor.execute("select current_database()")
db_name = cursor.fetchone()[0]
Related
Now, I have a study about python sqlite3 database. I think it is very simple problem but not allow next step. Could help me?
There is print OK on vscode terminal, but not revised to DB file. I'm searching several times but I can not fix it.
If I execute the code, it not sorting on DB files.
import sqlite3
conn = sqlite3.connect('sqliteDB1.db')
cursor = conn.cursor()
cursor.execute("SELECT * FROM member")
temp123 = cursor. fetchall()
print(temp123)
cursor.execute("SELECT * FROM member ORDER BY -code")
temp321 = cursor.fetchall()
conn.commit
print(temp321)
conn.close()
A select statement just returns data from a database, it will not modify it. Moreover, tables in SQL databases are inherently unordered sets. They have no intrinsic value, and you should never rely on the order of the rows that happens to be returned unless you explicitly sort it with an order by clause.
I am trying to select data from our main database (postgres) and insert it into a temporary sqlite database for some comparision, analytics and reporting. Is there an easy way to do this in Python? I am trying to do something like this:
Get data from the main Postgres db:
import psycopg2
postgres_conn = psycopg2.connect(connection_string)
from_cursor = postgres_conn.cursor()
from_cursor.execute("SELECT email, firstname, lastname FROM schemaname.tablename")
Insert into SQLite table:
import sqlite3
sqlite_conn = sqlite3.connect(db_file)
to_cursor = sqlite_conn.cursor()
insert_query = "INSERT INTO sqlite_tablename (email, firstname, lastname) values %s"
to_cursor.some_insert_function(insert_query, from_cursor)
So the question is: is there a some_insert_function that would work for this scenario (either using pyodbc or using sqlite3)?
If yes, how to use it? Would the insert_query above work? or should it be modified?
Any other suggestions/approaches would also be appreciated in case a function like this doesn't exist in Python. Thanks in advance!
You should pass the result of your select query to execute_many.
insert_query = "INSERT INTO smallUsers values (?,?,?)"
to_cursor.executemany(insert_query, from_cursor.fetchall())
You should also use a parameterized query (? marks), as explained here: https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.execute
If you want to avoid loading the entire source database into memory, you can use the following code to process 100 rows at a time:
while True:
current_data = from_cursor.fetchmany(100)
if not current_data:
break
to_cursor.exectutemany(insert_query, current_data)
sqlite_conn.commit()
sqlite_conn.commit()
You can look at executemany from pyodbc or sqlite. If you can build a list of parameters from your select, you can pass the list to executemany.
Depending on the number of records you plan to insert, performance can be a problem as referenced in this open issue. https://github.com/mkleehammer/pyodbc/issues/120
I'm trying to populate a couple databases with psycopg2 within a server I am not the root user of (don't know if it's relevant or not). My code looks like
import json
from psycopg2 import connect
cors = connect(user='jungal01', dbname='course')
req = connect(user="jungal01", dbname='requirement')
core = cors.cursor()
reqs = req.cursor()
with open('gened.json') as gens:
geneds = json.load(gens)
for i in range(len(geneds)):
core.execute('''insert into course (number, description, title)
values({0}, {1}, {2});''' .format(geneds[i]["number"], geneds[i]['description'], geneds[i]['title'] ))
reqs.execute('''insert into requirement (fulfills)
values({0});''' .format(geneds[i]['fulfills'] ))
db.commit()
when I execute the code, I get the above pycopg2 error. I know that these particular databases exist, but I just can't figure out why it won't connect to my databases. (side quest, I am also unsure about that commit statement. Should it be in the for loop, or outside of it? It suppose to be database specific?)
First, you have db is not a defined variable, so you code shouldn't run completely anyway.
\list on this server is a bunch of databases full of usernames, of which my username is one
Then the following is how you should connect. To a database, not a table, and the regular pattern is to put the database name, and then the user/pass.
A "schema" is a loose term in relational database. Both tables and databases have schemas, but you seem to be expecting to connect to a table, not a database.
So, try this code with an attempt at fixing your indentation and SQL injection problem -- See this documentation
Note that you first must have created the two tables in the database you are connecting to.
import json
from psycopg2 import connect
username = 'jungal01'
conn = connect(dbname=username, user=username)
cur = conn.cursor()
with open('gened.json') as gens:
geneds = json.load(gens)
for g in geneds:
cur.execute('''insert into course (number, description, title)
values(%(number)s, %(description)s, %(title)s);''', g)
cur.execute('''insert into requirement (fulfills)
values(%(fulfills)s);''', g)
conn.commit()
Allen, you said: "in postgres, tables are databases." That's wrong. Your error message results from this misunderstanding. You want to connect to a database, and insert into a table that exists in that database. You're trying to insert into a database -- a nonsensical operation.
Make sure you are giving the catalog name as database name and not the schema's under catalog.
Catalog is confusing and quite unnecessary. More details below: What's the difference between a catalog and a schema in a relational database?
I would like to check if a database table exists or not, but I don't know how to do.
I wrote (for example with SQLite, although I use MySQL mainly),
import sqlite3
table_name = "some_table"
connection = sqlite3.connect(db)
cursor = connection.cursor()
table_check = "SELECT name FROM sqlite_master WHERE type='table' AND name={};".format(table_name)
if not cursor.execute(table_check).fetchone(): # if the table doesn't exist
# OR if cursor.execute(table_check).fetchone() == "":
create_table()
else:
update_table()
But, an Error occured and I cannot proceed.
sqlite3.OperationalError: no such column: some_table
I read several Q&A here, but I couldn't get those.
Any advice can help me.
Thank you.
Python 3.5.1
The answer is depending on what rdbms product (mysql, sqlite, ms sql, etc.) you use.
You are getting this particular error in your above query because you do not enclose the value of table_name variable in single quotes.
In mysql you can use information_schema.tables table to query if a table exists.
I'm using MysqlDB. Does it provide a way to execute multiple SELECT queries like mysqli_multi_query does? If not, is there a python library that would allow that?
There is executemany, but that's not what I'm looking for. I'm working with Sphinx and trying to get its batch queries to work.
I spent some time to dig in the source code of MySQLdb and the answer is YES you can do multiple queries with it:
import MySQLdb
db = MySQLdb.connect(user="username", db="dbname")
cursor = db.cursor()
batch_queries = '''
SELECT * FROM posts WHERE id=1;
SELECT * FROM posts WHERE id=2;
'''
cursor.execute(batch_queries)
print cursor.fetchone()
while cursor.nextset(): # iterate to next result set if there is any
print cursor.fetchone()
cursor.close()
Tested successfully in my localhost. Hope it helps.