I am aware a similiar question exists. It has not been marked as answered yet and I tried all suggestions so far. I am also not native speaker, please excuse spelling mistakes.
I have written a small class in python to interact with a SQL Database.
Now I want to be able to connect to either SQL or MYSQL Database with the same functionalities.
It would be perfect for me to just change the connection type in the instance initiation to keep my class maintainable. Else I would need to create a seconde class using for example the mysql.connector, which would result in two classes with nearly the same structure and content.
This is how I tried to use pyodbc so far:
conn = pyodbc.connect('Driver={SQL Server};'
'Server=xyzhbv;'
'Database=Test;'
'ENCRYPT=yes;'
'UID=root;'
'PWD=12345;')
Please note that I changed all credentials.
What do I need to change to use pyodbc for MySQL?
Is that even possible?
Or
Can I use both libaries within one class without confusing? (they share function names)
Many Thanks for any help.
Have a great day.
I'm trying to use a cursor to open a database and read a table using Python, however I keep getting this error:
sqlite3.OperationalError: no such table: table_name
I can also see that a new .db file is created with the same name as the one I want to open, except that it's empty.
This has worked before on a different database although my code did not close the connection to that database when I ran it the first time.
Could it be that the connection is still open, and that is why I am unable to run the code on a different database? If so, how can I make sure that connection is closed?
If this is not the case, would it be possible for someone to shed some light on this?
In db.py,I can use a function(func insert) insert data into sqlite correctly.
Now I want to insert data into sqlite through python-fastcgi, in
fastcgi (just named post.py ) I can get the request data correctly,but
when I call db.insert,it gives me internal server error.
I already did chmod 777 slqite.db. Anyone know whats problem?
Ffinally I found the answer:
the sqlite3 library needs write permissions also on the directory that contains it, probably because it needs to create a lockfile.
Therefor when I use sql to insert data there is no problem, but when I do it through web cgi,fastcgi etc）to insert data there would be an error.
Just add write permission to the directory.
Ok first, please assume that this is the first time I will be writing a single alphabet of code in SQL.. so please please please... it would be very kind if you can explain me each step. :)
I am using mac for this development.
So in the desktop, I have a huge (1.5GB) dumpfile of a database.
I have mysqlworkbench (yes I have never worked in that either :( )
And I have installed MySQLdb.
So, basically what I want to do is use the data in the database from python.
So I have python.. mysqldb to connect to db.. huge db and mysqlworkbench..
Now I assume, that this dumpfile is useless as its not in form of database..
so how do I "mount" this dump to a database..(mysqlworkbench)
After that how do I query from python..
(like the port number.. username , password!! ? )
It would be of huge help if anyone can help me.. I have been stuck in this since morning.. :(
In order to use the data in the file, it needs to be imported into the database. (Think of the file as a recipe for MySQL to make a database. Now you need to tell MySQL to make the database from the recipe).
You can import the database using command line, a python script or even MySQL workbench. However, due to the size of the file, using MySQL workbench could be a problem (Note: I am not familiar with MySQL workbench).
To import the database with the command line use the command:
mysql -u <username> -p -h localhost king_tracking < <filename>
To actually use the database with python, there are several step by step tutorials available, easily accessible from a google search. A basic script is (from here)
import MySQLdb
conn = MySQLdb.connect (host = "localhost",
user = "testuser",
passwd = "testpass",
db = "test")
cursor = conn.cursor ()
cursor.execute ("SELECT VERSION()")
row = cursor.fetchone ()
print "server version:", row[0]
cursor.close ()
conn.close ()
This just shows the version of MySQL, however if
"SELECT VERSION()"
is replaced by your own query, like
"SELECT * FROM <tablename> LIMIT 0,30"
you can execute your own queries.
In order to understand the tutorials on interfacing python and MySQL, you should be familiar with both separately. A good SQL tutorial is the one at W3schools.
The problem with creating a table is separate from the original question, but may need to be addressed before trying to import the file into the database.
I have created a Python module that creates and populates several SQLite tables. Now, I want to use it in a program but I don't really know how to call it properly. All the tutorials I've found are essentially "inline", i.e. they walk through using SQLite in a linear fashion rather than how to actually use it in production.
What I'm trying to do is have a method check to see if the database is already created. If so, then I can use it. If not, an exception is raised and the program will create the database. (Or use if/else statements, whichever is better).
I created a test script to see if my logic is correct but it's not working. When I create the try statement, it just creates a new database rather than checking if one already exists. The next time I run the script, I get an error that the table already exists, even if I tried catching the exception. (I haven't used try/except before but figured this is a good time to learn).
Are there any good tutorials for using SQLite operationally or any suggestions on how to code this? I've looked through the pysqlite tutorial and others I found but they don't address this.
Don't make this more complex than it needs to be. The big, independent databases have complex setup and configuration requirements. SQLite is just a file you access with SQL, it's much simpler.
Do the following.
Add a table to your database for "Components" or "Versions" or "Configuration" or "Release" or something administrative like that.
CREATE TABLE REVISION(
RELEASE_NUMBER CHAR(20)
);
In your application, connect to your database normally.
Execute a simple query against the revision table. Here's what can happen.
The query fails to execute: your database doesn't exist, so execute a series of CREATE statements to build it.
The query succeeds but returns no rows or the release number is lower than expected: your database exists, but is out of date. You need to migrate from that release to the current release. Hopefully, you have a sequence of DROP, CREATE and ALTER statements to do this.
The query succeeds, and the release number is the expected value. Do nothing more, your database is configured correctly.
AFAIK an SQLITE database is just a file.
To check if the database exists, check for file existence.
When you open a SQLITE database it will automatically create one if the file that backs it up is not in place.
If you try and open a file as a sqlite3 database that is NOT a database, you will get this:
"sqlite3.DatabaseError: file is encrypted or is not a database"
so check to see if the file exists and also make sure to try and catch the exception in case the file is not a sqlite3 database
SQLite automatically creates the database file the first time you try to use it. The SQL statements for creating tables can use IF NOT EXISTS to make the commands only take effect if the table has not been created This way you don't need to check for the database's existence beforehand: SQLite can take care of that for you.
The main thing I would still be worried about is that executing CREATE TABLE IF EXISTS for every web transaction (say) would be inefficient; you can avoid that by having the program keep an (in-memory) variable saying whether it has created the database today, so it runs the CREATE TABLE script once per run. This would still allow for you to delete the database and start over during debugging.
As #diciu pointed out, the database file will be created by sqlite3.connect.
If you want to take a special action when the file is not there, you'll have to explicitly check for existance:
import os
import sqlite3
if not os.path.exists(mydb_path):
#create new DB, create table stocks
con = sqlite3.connect(mydb_path)
con.execute('''create table stocks
(date text, trans text, symbol text, qty real, price real)''')
else:
#use existing DB
con = sqlite3.connect(mydb_path)
...
Sqlite doesn't throw an exception if you create a new database with the same name, it will just connect to it. Since sqlite is a file based database, I suggest you just check for the existence of the file.
About your second problem, to check if a table has been already created, just catch the exception. An exception "sqlite3.OperationalError: table TEST already exists" is thrown if the table already exist.
import sqlite3
import os
database_name = "newdb.db"
if not os.path.isfile(database_name):
print "the database already exist"
db_connection = sqlite3.connect(database_name)
db_cursor = db_connection.cursor()
try:
db_cursor.execute('CREATE TABLE TEST (a INTEGER);')
except sqlite3.OperationalError, msg:
print msg
Doing SQL in overall is horrible in any language I've picked up. SQLalchemy has shown to be easiest from them to use because actual query and committing with it is so clean and absent from troubles.
Here's some basic steps on actually using sqlalchemy in your app, better details can be found from the documentation.
provide table definitions and create ORM-mappings
load database
ask it to create tables from the definitions (won't do so if they exist)
create session maker (optional)
create session
After creating a session, you can commit and query from the database.
See this solution at SourceForge which covers your question in a tutorial manner, with instructive source code :
y_serial.py module :: warehouse Python objects with SQLite
"Serialization + persistance :: in a few lines of code, compress and annotate Python objects into SQLite; then later retrieve them chronologically by keywords without any SQL. Most useful "standard" module for a database to store schema-less data."
http://yserial.sourceforge.net
Yes, I was nuking out the problem. All I needed to do was check for the file and catch the IOError if it didn't exist.
Thanks for all the other answers. They may come in handy in the future.