数据库代写 | Introduction to Python for accessing SQLite

本次代写主要为Python&sqlite数据库操作的Lab

Background Knowledge

By now you should have some experience of basic SQL commands such as “CREATE”, “SELECT” and “INSERT”. This lab, you will learn how to query data in SQLite from Python.

We recommend you use Repl.it to practise these queries. However, if you wish to complete this worksheet on your own PC you will have to install Python version 3 and the sqlite3 python module. Details of how to install these pieces of software are beyond the scope of this tutorial, but can be easily found from many internet sites. A number of “dynamic tutorials” that demonstrate the installation of this software are provided in the software section of this website.

Note that this tutorial is not intended to be exhaustive, it is a simple introduction. You should ensure that you access the other resources available on the internet and in relevant textbooks to find out more.

 

In this lab you will be,

  1. Creating a Python program on Repl

Click new repl button on the top menu and then search Python. The main.py will be created in your repl repository.

 

  1. The first script

The following is the typical “Hello World” program for Python. Use an editor to type it in as shown below;

print (“Hello World!”)

You should see a response text “Hello World”.

  1. Connecting to a sqlite3 database

We are going to be using an example database in this session. Since we have learnt to use a Python script, we may as well use Python to set up the example database. Type (or cut-and-paste) the following the main.py file.

 

import sqlite3

conn = sqlite3.connect(‘store’)

conn.execute(“CREATE TABLE ‘pet’ (name VARCHAR(20), owner VARCHAR(20), species VARCHAR(20), sex CHAR(1), checkups SMALLINT UNSIGNED, birth DATE, death DATE)”)

 

 

When you run the script, store.db file will be automatically created. You will not see any data in the database just yet.

Before moving on, take some time to have a look again at the script you have just run. Go through the script and put a comment above each statement that describes what you think the statement is doing. Feel free to post your repl.it link in the “General Q&A” and compare what you think with another member of your class.

 

Try running the script more than one time. What did you get?

 

Now let’ try this script:

 

import sqlite3

conn = sqlite3.connect(‘store’)

print (“Database has been created”)

 

conn.execute(“DROP TABLE IF EXISTS pet”)

 

conn.execute(“CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), species VARCHAR(20), sex CHAR(1), checkups SMALLINT UNSIGNED, birth DATE, death DATE)”)

 

print (“Table created successfully”)

 

  1. Inserting Data

Inserting data into a table in the database is not the simplest of the things you might want to do but is clearly fundamental to any database work with Python.

A new record is inserted into a table using the INSERT query. An example is the following:

 

“INSERT INTO pet VALUES (1, ‘Fluffy’, ‘Alice’, ‘cat’, ‘f’, 5, ‘2001-02-04’, null)” 

It is possible to specify which fields data will be inserted into too. Default values will be supplied in any fields not used, as long as these default values do not contravene the data description of the record.

“INSERT INTO pet (name, owner, species, birth) VALUES (‘Fluffy’, ‘Alice’, ‘cat’, ‘2001-02-04’)”

Now let’s use this knowledge to insert some data. Consider the following Python script:

conn.execute(“INSERT INTO pet (name,owner,species,sex,checkups,birth,death)VALUES \

(‘Fluffy’,’Harold’,’cat’,’f’,5,’2001-02-04′,”)”)

 

conn.execute(“INSERT INTO pet (name,owner,species,sex,checkups,birth,death)VALUES \

(‘Claws’,’Gwen’,’cat’,’m’,2,’2000-03-17′,”)”)

 

conn.commit()

print(“Records created successfully”)

print(“Total number of rows created :”, conn.total_changes)

 

What do you think will happen when the script is executed?


程序代写代做C/C++/JAVA/安卓/PYTHON/留学生/PHP/APP开发/MATLAB


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