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();

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

    # 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()

Answer 1

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.