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() 

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.

Answer 2

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()