Python Database - CRUD Operations

Python Database - CRUD
1. CREATE,INSERT
2. READ
3. UPDATE
4. DELETE
Elangovan Tech Notes 1

INTRODUCTION TO SQLITE3
SQLITE3
• It is a lightweight and relational database system (RDBMS) with zero
configuration
• It is a server-less database that we can use within almost all programming
languages.
• Server-less means there is no need to install a separate server to work with
SQLite. So we can connect directly with database.
• Permanent storage
• Entire database will be saved in single text file.
• It is used in stand alone applications.
• It supports the standard RDBMS like SQL syntax, transactions and prepared
statements.

SQLITE3-DB Browser
SQLITE3-DB Browser
• Download the DB Browser software “DB.Browser.for.SQLite-3.11.0-beta3-win64”
for visual
• This is optional one. It is a high quality, visual and open source tool used for
creating, designing and editing the database files which are compatible with
SQLite database.
Home page of SQLite DB
Browser

SQLITE3-Requirements-Setup
SQLITE3
• Download the following sqlite3 softwares in the SQLite home page
1. Download sqlite-dll-win64-x64-3360000.zip (32 bit) or sqlite-dll-win64-
x64-3360000.zip (64bit)
2. Download sqlite-tools-win32-x86-3360000.zip
• Extract the zip files listed above and add the extracted contents in the folder of
your computer like c/sqlite
Path of sqlite

Popular Usages of SQLite
SQLITE3
• This database can be used for the following areas
1. Database for Gadgets
• Mobiles, PDAs, MP3 Players, etc,…
2. Website Database
3. Internal Database (Temporary Database)

SQLITE3-DB-OPERATIONS
SQLITE3
• Python supports the following operations mentioned below with help of sqlite3
lightweight database. They are
1. Database Creation
2. Table Creation
3. Record Insertion
4. Record Deletion
5. Record Updation
6. Table Retrieval (Retrieval via cursor object)

Cursor
Importance of Cursor
• To retrieve the SQLite statements in python code, we need a cursor object. We
can create it by using the built-in instance method like cursor() of connection
object
• To execute the sql query, first we should establish the database connection and
then create an object of the cursor using the connection object as shown in
below
Cursor Object Creation
• We can execute any sql query using the execute() method of cursor object.
// connect and create the database using connect() method
con=sqlite3.connect(‘ganesh.db’)
// create the cursor object using cursor() method of connection object
cc=con.cursor()

Important Methods-SQLite
BUILT-IN METHODS
• SQLite provides several methods for CRUD. They are
1. connect()  connecting DB
2. execute()  executing SQL queries like insert, delete, select,…
3. cursor()  needed for data retrieval (use of select query)
4. fetchall()  read all the records from table
5. commit()  saves the current transactions
6. close()  close the DB connection
1. connect(database-name)
• It is used to connect the database with specified path
• It takes one plus arguments where first argument is the name of the database
• Return type : Connection

Important Methods-SQLite- (Con)
BUILT-IN METHODS
2. execute(query, optional parameters)
• It is an instance method of connection object
• It is used to execute sql queries such as select, insert, delete, update queries
• It will execute only one sql query at a time
• It takes one plus arguments. Where first argument is the sql query and second
argument can be optional parameters
• Return type : Cursor
3. cursor()
• It is used to create a cursor object which will be used throughout of your
database with python
• It takes one optional argument called Cursor class
• Return type : Cursor Elangovan Tech Notes 9

BUILT-IN METHODS
4. fetchall()
• It is an instance method of cursor object
• It is used to read all the rows of a table (records) returning a list type. An empty
list will be returned, if no rows are available
• Return type : list
5. commit()
• This method is used to save the current transaction. If you don’t call this method
for DML queries like insert, delete, update,etc, then these changes will not be
reflected in the database connection.
• Return type : NoneType

BUILT-IN METHODS
6. close()
• It is used to close the database connection and returns nothing
• It is a note that, if you close the database connection without calling commit()
method, then the changes will not be saved (changes will be lost)
• Return type : NoneType
5. total_changes
• It is an instance proprty of connection object
• This property just returns the total number of table rows that have been
inserted, deleted and modified
• Return type : int

Database Creation
Creating database using Sqlite3
• To create a database, just call connect() method SQLite3 module, then the
database will be automatically created based on the specified path in your
machine.
• This database is created and saved on disk.

Database Creation – (Con)
SOURCE CODE
import sqlite3
# create the database by starting the connection with sqlite
try:
con=sqlite3.connect("ganesh.db")
print("Database is successfully created...")
except Error:
print("Error in creating the database")
finally:
con.close()
Close the database using close()
method
Connect and create the new
database like ganesh.db in the
current folder
This is the name of the database

OUTPUT
Use the command to run the python code:
python <filename.py>
(OR)
py <filename.py>

VERIFICATION FOR NEWLY CREATED DATABASE

1. Table Creation using Python
CREATING A TABLE
• To create a table in sqlite3 via python, use the following below
1. Create a connection object using connect() method of sqlite3
2. Define the create query for new table and store it in variable
3. Call this query using execute() method of connection object and then the new
table will be created in the input database used

Table Creation using Python – (Con)
SOURCE CODE
import sqlite3
print("-----------------------------")
print("tTable Creation")
print("-----------------------------")
# sql create query and use if not exists for the table verification
sql="create table if not exists stud(id integer primary key, name text, dept text, cgpa
real);"
# create the database and return the connection object
print("Opened Database Successfully")
# create a new table in the database using execute()
con.execute(sql)
print("Table is successfully created...")
con.close()
SQL Create query: create table if already not
existed using if not exists condition
Running the query using execut()
method will create a new table

Table Creation using Python – (Con)
OUTPUT

Table Verification in DB Browser for SQlite

1.1 Data Insertion
Data Insertion
• To insert the data into a table in sqlite3 via python, use the following below
1. Create a connection object
2. Define the insert query based on your requirement and call this query using
execute() method of connection object and then record will be inserted
3. Commit the changes using commit() method of connection object
4. Close the database using close() method

1.1 Data Insertion – (Con)
SOURCE CODE
print("---------------------------------")
print("tDB Data Insertion")
print("---------------------------------")
# connect & open existing DB
print("Opened Database Sucessfully")
# add the insert queries as you want in the execute() method of connection object
con.execute("insert into stud values(1,'Sachin','IT',9.55)")
con.execute("insert into stud values(5,'John','CS',7.55)")
con.execute("insert into stud values(7,'Rohit','IT',9.90)")
con.execute("insert into stud values(12,'Venkat','CS',9.95)")
con.execute("insert into stud values(14,'Dravid','IT',8.70)")
Execution of Insert queries using
execute() method of connection
object
Open the existing
Database

SOURCE CODE
# commit the changes
con.commit()
print("Five rows/records are successfully inserted...")
# close the DB
con.close()
Close the database using
close() method
Saves the DB changes

OUTPUT

PROOF FOR DATA INSERTION OPERATION [DB Browser for SQLite – Tool]

2. Data Retrieval (Read)
DATA RETRIEVAL
• To display the data from database table, do the following things mentioned
below
1. Connect and open the existing database using connect() method
2. Create cursor object for data retrieval using connection object
3. Execute the select query using cursor object with execute() method
4. Read all data from table using cursor and store them to list based result set
5. Iterate the result set via looping (for or while loop)
6. Display the records (via rows or columns)

2. Data Retrieval (Read) – (Con)
SOURCE CODE
import sqlite3
print("----------------------------------")
print("tData Retrieval")
print("----------------------------------")
# connect and open the existing DB
# create the cursor object from connection object
cc=con.cursor()
sql="select * from stud"
# execute the sql query using cursor object
cc.execute(sql)
# read all the records from table using fetchall() method and store the result in
result set variable “rs”
rs=cc.fetchall()
Open the existing DB
Execute the select query using
execute() via cursor object
Select query
Read all the rows using fetchall() method

SOURCE CODE
print("ID Name Dep CGPA")
for row in rs:
print(row[0],row[1],row[2],row[3])
# close the DB
con.close()
Iterate the records ONE BY ONE
from result set (rs) using for loop
The cursor initially points to 0th row before
loop. In the loop, it starts from 1st row and
ends at last row if next row is unavailable.
Here column names are labeled with index numbers 0 to n-1
Where
row[0] -> First Column, row[1] -> Second Column
row[2] -> Third Column, row[3] -> Fourth Column
Close
the DB

OUTPUT

3. Data Updation (CRUD)
DATA UPDATE
• To update the record from database table, do the following things mentioned below
2. Define the update query and substitute it in the execute() method of
connection object
3. Execute the query using execute() method of connection object
5. Close the DB.

3. Data Updation (CRUD) – (Con)
SOURCE CODE
import sqlite3
print("---------------------------------")
print("tData Updation")
print("---------------------------------")
# connect and open the existing DB
# define the update query
usql="update stud set name='Velan', dept='SE' where id=5"
# execute the update query using execute() method of connection object
con.execute(usql)
con.commit()
Update the record number 5

SOURCE CODE
print("One Record is successfully updated...")
print("Total Rows are affected...",con.total_changes)
# close the DB
con.close()

OUTPUT

Before Update (Table Data) [DB Browser for SQLite – Tool]

After Update (Table Data) [DB Browser for SQLite – Tool]

4. Data Deletion (CRUD)
DATA DELETION
• To delete the record from database table, do the following things mentioned below
2. Define the update query and substitute it in the execute() method of
connection object
3. Execute the query using execute() method of connection object
5. Close the DB.

4. Data Deletion (CRUD) – (Con)
SOURCE CODE
import sqlite3
print("-------------------------------")
print("tData Deletion")
print("-------------------------------")
# connect and open the DB
# delete query
dsql="delete from stud where id=7"
# execute the delete query using execute() method of connection object
con.execute(dsql)
con.commit()
Delete the 7th record
Save this transaction in DB
using commit() method

SOURCE CODE
print("One Record was deleted successfully...")
print("Total Rows are affected",con.total_changes)
# close the DB
con.close()
Display the total count of rows
affected by delete query

OUTPUT

Before Delete (Table Data) [DB Browser for SQLite – Tool]

After Delete (Table Data) [DB Browser for SQLite – Tool]
Before deletion, total records were 5.
After the deletion of one record, the
total count of records are 4.

Thank You

Live Demo
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by step
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Python Database - CRUD Operations

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