Newbie to sql and sqlite.
I'm trying to save a database, then copy the file.db to another folder and open it. So far I created the database, copy and pasted the file.db to another folder but when I try to access the database the output says that it is empty.
So far I have
from pysqlite2 import dbapi2 as sqlite
conn = sqlite.connect('db1Thu_04_Aug_2011_14_20_15.db')
c = conn.cursor()
print c.fetchall()
and the output is
[]
You need something like
c.execute("SELECT * FROM mytable")
for row in c:
#process row
I will echo Mat and point out that is not valid syntax. More than that, you do not include any select request (or other sql command) in your example. If you actually do not have a select statement in your code, and you run fetchall on a newly created cursor, you can expect to get an empty list, which seems to be what you have.
Finally, do make sure that you are opening the file from the right directory. If you tell sqlite to open a nonexistent file, it will happily create a new, empty one for you.
Related
I think I've lost my mind. I have created a python script to read a temp table in SQL SSMS. While testing, we found out that python is able to query and read the table even when it's not there/queryable in SSMS. I believe the DF is storing in cache or something but let me break down the problem into steps:
Starting point, the temp table is present in SSMS, MAIN_DF = python.read_sql('SELECT Statement') and stored in DF and saved to excel file (using ExcelWriter)
We delete the temp table in SQL, then run the python script again. To make sure, we use THE SAME 'SELECT' statement found in the python script in SSMS and it displays 'Invalid object name' which is correct because the table has been dropped. BUT when I run the python script again, it is able to query the table and get the same results it had before! It should be throwing the same error as SSMS because the table isn't there! Why isn't python starting from scratch when I run it? It seems to be holding information over from the initial run. How do I ensure I am starting from scratch every time I run it?
I have tried many things including starting the script with blank DF's so they should not have anything held over. 'MAIN_DF = pd.DataFrame()'. I have tried deleting the DF's at the end as well. 'del MAIN_DF'
I don't understand what is happening..
try:
conn = pyodbc.connect(r'Driver={SQL Server};Server=GenericServername;Database=testdb;Trusted_Connection=yes;')
print('Connected to SQL: ' + str(datetime.now()))
MAIN_DF = pd.read_sql('SELECT statement',conn)
print('Queried Main DF: ' + str(datetime.now()))
It's because I didn't close the connection conn.close() so it was cached in the memory and SQL didn't perform / close it
I have a very big database and I want to send part of that database (1/1000) to someone I am collaborating with to perform test runs. How can I (a) select 1/1000 of the total rows (or something similar) and (b) save the selection as a new .db file.
This is my current code, but I am stuck.
import sqlite3
import json
from pprint import pprint
conn = sqlite3.connect('C:/data/responses.db')
c = conn.cursor()
c.execute("SELECT * FROM responses;")
Create a another database with similar table structure as the original db. Sample records from original database and insert into new data base
import sqlite3
conn = sqlite3.connect("responses.db")
sample_conn = sqlite3.connect("responses_sample.db")
c = conn.cursor()
c_sample = sample_conn.cursor()
rows = c.execute("select no, nm from responses")
sample_rows = [r for i, r in enumerate(rows) if i%10 == 0] # select 1/1000 rows
# create sample table with similar structure
c_sample.execute("create table responses(no int, nm varchar(100))")
for r in sample_rows:
c_sample.execute("insert into responses (no, nm) values ({}, '{}')".format(*r))
c_sample.close()
sample_conn.commit()
sample_conn.close()
Simplest way to do this would be:
Copy the database file in your filesystem same as you would any other file (e.g. ctrl+c then ctrl+v in windows to make responses-partial.db or something)
Then open this new copy in an sqlite editor such as http://sqlitebrowser.org/ run the delete query to remove however many rows you want to. Then you might want to run compact database from file menu.
Close sqlite editor and confirm file size is smaller
Email the copy
Unless you need to create a repeatable system I wouldn't bother with doing this in python. But you could perform similar steps in python (copy the file, open it it run delete query, etc) if you need to.
The easiest way to do this is to
make a copy of the database file;
delete 999/1000th of the data, either by keeping the first few rows:
DELETE FROM responses WHERE SomeID > 1000;
or, if you want really random samples:
DELETE FROM responses
WHERE rowid NOT IN (SELECT rowid
FROM responses
ORDER BY random()
LIMIT (SELECT count(*)/1000 FROM responses));
run VACUUM to reduce the file size.
I have been given an SQLite file to exam using python. I have imported the SQLite module and attempted to connect to the database but I'm not having any luck. I am wondering if I have to actually open the file up as "r" as well as connecting to it? please see below; ie f = open("History.sqlite","r+")
import sqlite3
conn = sqlite3.connect("history.sqlite")
curs = conn.cursor()
results = curs.execute ("Select * From History.sqlite;")
I keep getting this message when I go to run results:
Operational Error: no such table: History.sqlite
An SQLite file is a single data file that can contain one or more tables of data. You appear to be trying to SELECT from the filename instead of the name of one of the tables inside the file.
To learn what tables are in your database you can use any of these techniques:
Download and use the command line tool sqlite3.
Download any one of a number of GUI tools for looking at SQLite files.
Write a SELECT statement against the special table sqlite_master to list the tables.
I have a program in Python composed of 4 source files. One of them is the main file which imports the other 3. As I work with a small Sqlite database, I am creating tables in one of the "secondary" source files, but when I access the database again from the main source file, the tables just populated before are empty.
Can I save the tables' content in a more consistent way? I am quite surprised with what is happening.
So in the main file I typed:
conn = sqlite3.connect("bayes.db")
cur = conn.cursor()
cur.execute("select count(*) from TableA")
print cur.fetchone()
The result is 0 (rows).
Just before, in another source file I do the same thing and get size=8 of TableA.
You must call the commit function in order to save your changes in the database. You can see the full documentation here: http://docs.python.org/2/library/sqlite3.html#sqlite3.Connection.commit
I tried researching the answer but was not able to find a good solution. I have files with strange extensions .res. I was told that they are MS Access files. Not sure if they are the same as .mdb but I was able to open them in MS Access. How can I open those files, extract necessary data, sort that data and produce .csv file? I tried using this script: http://mazamascience.com/WorkingWithData/?p=168 and mdb tools on Linux. I got some output with errors in terminal but all the files produced were blank. It could be due to encoding. I am not sure. The file is in ASCII encoding I think.
Error: Table fo_Table
Smart_Battery_Data_Table
MCell_Aci_Data_Table
Aux_Global_Data_Table
Smart_Battery_Clock_Stretch_Table
does not exist in this database.
On Windows I have no idea how to do it. My first step for now is just to dump the necessary table from that database file into .csv. But ideally I need the script to take the file, sort it, extract necessary data, do some calculations (like data in one column divided by data in another column) and save all that stuff into nice .csv.
Thanks a lot. I am not an experienced programmer so please have mercy.
Using the generic pyodbc library should do it. Looks like it has already an embedded MS access driver. This question can probably help you out.
I dont have any MS Access database files with me (It has been ages that I dont have to work with them), but following the examples your code should be something like this:
import pyodbc
db_file = r'''/path/to/the/file.res'''
user = 'admin'
password = 'password'
odbc_conn_str = 'DRIVER={Microsoft Access Driver (*.mdb)};DBQ=%s;UID=%s;PWD=%s' % (db_file, user, password)
conn = pyodbc.connect(odbc_conn_str)
cursor = conn.cursor()
cursor.execute("select * from table order by some_column")
for row in cursor.fetchall():
print ", ".join((row.column1, row.column2, row.columnN))