reading external sql script in python

Question

I am working on a learning how to execute SQL in python (I know SQL, not Python).

I have an external sql file. It creates and inserts data into three tables 'Zookeeper', 'Handles', 'Animal'.

Then I have a series of queries to run off the tables. The below queries are in the zookeeper.sql file that I load in at the top of the python script. Example for the first two are:

--1.1

SELECT ANAME,zookeepid
FROM ANIMAL, HANDLES
WHERE AID=ANIMALID;

--1.2

SELECT ZNAME, SUM(TIMETOFEED)
FROM ZOOKEEPER, ANIMAL, HANDLES
WHERE AID=ANIMALID AND ZOOKEEPID=ZID
GROUP BY zookeeper.zname;

These all execute fine in SQL. Now I need to execute them from within Python. I have been given and completed code to read in the file. Then execute all the queries in the loop.

The 1.1 and 1.2 is where I am getting confused. I believe in the loop this is the line where I should put in something to run the first and then second query.

result = c.execute("SELECT * FROM %s;" % table);

but what? I think I am missing something very obvious. I think what is throwing me off is % table. In query 1.1 and 1.2, I am not creating a table, but rather looking for a query result.

My entire python code is below.

import sqlite3
from sqlite3 import OperationalError

conn = sqlite3.connect('csc455_HW3.db')
c = conn.cursor()

# Open and read the file as a single buffer
fd = open('ZooDatabase.sql', 'r')
sqlFile = fd.read()
fd.close()

# all SQL commands (split on ';')
sqlCommands = sqlFile.split(';')

# Execute every command from the input file
for command in sqlCommands:
    # This will skip and report errors
    # For example, if the tables do not yet exist, this will skip over
    # the DROP TABLE commands
    try:
        c.execute(command)
    except OperationalError, msg:
        print "Command skipped: ", msg


# For each of the 3 tables, query the database and print the contents
for table in ['ZooKeeper', 'Animal', 'Handles']:


    **# Plug in the name of the table into SELECT * query
    result = c.execute("SELECT * FROM %s;" % table);**

    # Get all rows.
    rows = result.fetchall();

    # \n represents an end-of-line
    print "\n--- TABLE ", table, "\n"

    # This will print the name of the columns, padding each name up
    # to 22 characters. Note that comma at the end prevents new lines
    for desc in result.description:
        print desc[0].rjust(22, ' '),

    # End the line with column names
    print ""
    for row in rows:
        for value in row:
            # Print each value, padding it up with ' ' to 22 characters on the right
            print str(value).rjust(22, ' '),
        # End the values from the row
        print ""

c.close()
conn.close()

What SQL query(s) are you supposed to execute, the 1.1 and 1.2 ones, or just get everything from every table? — Azeirah
– Azeirah, Commented Oct 20, 2013 at 1:28
I want to run 1.1 and 1.2 (plus I have about 6 others) from the .sql file. — mpg
– mpg, Commented Oct 20, 2013 at 1:34
I'm going a bit too fast I believe, do you need help understanding the code or do you need help editing your code to do something extra? — Azeirah
– Azeirah, Commented Oct 20, 2013 at 1:58
probably both. All the sql I need is in zookeeper.sql (and is suppose to stay there). The python code then is suppose read the sql file, create the tables, populates them (which I think I have done right), AND then execute the queries (ie 1.1, 1.2) above. — mpg
– mpg, Commented Oct 20, 2013 at 2:02

Vaggelis Manousakis · Accepted Answer · 2021-08-02 21:37:06Z

172

Your code already contains a beautiful way to execute all statements from a specified sql file

# Open and read the file as a single buffer
fd = open('ZooDatabase.sql', 'r')
sqlFile = fd.read()
fd.close()

# all SQL commands (split on ';')
sqlCommands = sqlFile.split(';')

# Execute every command from the input file
for command in sqlCommands:
    # This will skip and report errors
    # For example, if the tables do not yet exist, this will skip over
    # the DROP TABLE commands
    try:
        c.execute(command)
    except OperationalError, msg:
        print("Command skipped: ", msg)

Wrap this in a function and you can reuse it.

def executeScriptsFromFile(filename):
    # Open and read the file as a single buffer
    fd = open(filename, 'r')
    sqlFile = fd.read()
    fd.close()

    # all SQL commands (split on ';')
    sqlCommands = sqlFile.split(';')

    # Execute every command from the input file
    for command in sqlCommands:
        # This will skip and report errors
        # For example, if the tables do not yet exist, this will skip over
        # the DROP TABLE commands
        try:
            c.execute(command)
        except OperationalError, msg:
            print("Command skipped: ", msg)

To use it

executeScriptsFromFile('zookeeper.sql')

You said you were confused by

result = c.execute("SELECT * FROM %s;" % table);

In Python, you can add stuff to a string by using something called string formatting.

You have a string "Some string with %s" with %s, that's a placeholder for something else. To replace the placeholder, you add % ("what you want to replace it with") after your string

ex:

a = "Hi, my name is %s and I have a %s hat" % ("Azeirah", "cool")
print(a)
>>> Hi, my name is Azeirah and I have a Cool hat

Bit of a childish example, but it should be clear.

Now, what

result = c.execute("SELECT * FROM %s;" % table);

means, is it replaces %s with the value of the table variable.

(created in)

for table in ['ZooKeeper', 'Animal', 'Handles']:


# for loop example

for fruit in ["apple", "pear", "orange"]:
    print(fruit)
>>> apple
>>> pear
>>> orange

If you have any additional questions, poke me.

edited Aug 2, 2021 at 21:37

Vaggelis Manousakis

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answered Oct 20, 2013 at 2:12

Azeirah

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10 Comments

mpg Over a year ago

Happy to take my questions offline, but how do you poke on SOF? I plugged in what I think you were talking about and got a bunch of errors. So I am still not getting something. MPG

sage88 Over a year ago

This code will attempt to execute an empty string query for all sql documents. The trailing semicolon will make an empty string list element. Try: sqlCommands = filter(None, sqlFile.split(';'))

JeffSpicoli Over a year ago

This works until you have a text column in your SQL file that contains a ';'

Azeirah Over a year ago

@TrevorJ.Smith All code posted directly on StackOverflow is licensed under the Creative Commons license see this post for more info. I am not a lawyer though, consult an attorney if you think it might be necessary in your case.

Labo Over a year ago

@Azeirah Your answer can cause SQL injections, can you make it use the ? syntax for SQL formatting?

|

Lukas Loos · Accepted Answer · 2020-09-02 07:08:19Z

17

A very simple way to read an external script into an sqlite database in python is using executescript():

import sqlite3

conn = sqlite3.connect('csc455_HW3.db')

with open('ZooDatabase.sql', 'r') as sql_file:
    conn.executescript(sql_file.read())

conn.close()

answered Sep 2, 2020 at 7:08

Lukas Loos

1991 silver badge5 bronze badges

2 Comments

bonobo Over a year ago

can't this be done with two with statements?

Lukas Loos Over a year ago

I read it up and it seems like using sqlite3.connect() as a context manager does not close the connection when exiting the context (I read this blog but didn't try it) In the comments they mention a closing() function from contextlib module though which you could use for writing this with two with statements

Sindhukumari Parameswaran · Accepted Answer · 2021-07-24 21:58:27Z

1

First make sure that a table exists if not, create a table then follow the steps.

import sqlite3
from sqlite3 import OperationalError

conn = sqlite3.connect('Client_DB.db')
c = conn.cursor()

def execute_sqlfile(filename):
    
    c.execute("CREATE TABLE clients_parameters (adress text, ie text)")
    #
    fd = open(filename, 'r')
    sqlFile = fd.readlines()
    fd.close()
    lvalues = [tuple(v.split(';')) for v in sqlFile[1:] ]
    try:
        #print(command)
        c.executemany("INSERT INTO clients_parameters VALUES (?, ?)", lvalues)
    except OperationalError as msg:
        print ("Command skipped: ", msg)

execute_sqlfile('clients.sql')

print(c.rowcount)

answered Jul 24, 2021 at 21:58

Sindhukumari Parameswaran

3503 silver badges6 bronze badges

Comments

Steffen Moritz · Accepted Answer · 2020-07-22 15:26:15Z

-13

according me, it is not possible

solution:

import .sql file on mysql server
after
```
import mysql.connector
import pandas as pd
```
and then you use .sql file by convert to dataframe

edited Jul 22, 2020 at 15:26

Steffen Moritz

7,76811 gold badges41 silver badges57 bronze badges

answered Jul 22, 2020 at 15:02

Dhruv Vavliya

1

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