What does SQLite database contain?
SQLite Database has data stored in it in the form of tables.
What does a table contain?
It contains rows and columns.
A row is also called a record or tuple.
A column is also called an attribute.
Let's say we have a table called 'marks'.
What all columns can table of marks contain?
1. Year
2. Class
3. Subject
4. Marks
Four Basic Types of Operations We Do in Databases
Assuming you have a database with you:
Insert: To add or create a new record or tuple in your database.
Select: To read a records or tuples present in the database.
Update: To change an existing record or tuple in your database.
Delete: To remove or delete a record or tuple from the database.
Can be remembered using the acronym: CRUD for Create, Read, Update, Delete
Single File For Storing a Database
Note: SQLite uses a single file for storing data related a database. For example: we have two databases with us and there names are 'marks.db' and 'sharks.db'.
(base) ashish@ashish:~/Desktop/ws/sqlite_db$ ls
marks.csv marks.db sharks.db
(base) ashish@ashish:~/Desktop/ws/sqlite_db$
Creating a Database file and Creating a Table
(base) ashish@ashish:~$ sqlite3 sharks.db # Here, sqlit3 is your application and sharks.db is the filename for that application to open. SQLite version 3.39.3 2022-09-05 11:02:23 Enter '.help' for usage hints. sqlite> CREATE TABLE sharks(id integer NOT NULL, name text NOT NULL, sharktype text NOT NULL, length integer NOT NULL); INSERT INTO sharks VALUES (1, 'Sammy', 'Greenland Shark', 427); INSERT INTO sharks VALUES (2, 'Alyoshka', 'Great White Shark', 600); INSERT INTO sharks VALUES (3, 'Himari', 'Megaladon', 1800); sqlite> select * from sharks; 1|Sammy|Greenland Shark|427 2|Alyoshka|Great White Shark|600 3|Himari|Megaladon|1800
sqlite>
(base) ashish@ashish:~/Desktop/ws/sqlite_db$ sqlite3 sharks.db
SQLite version 3.39.3 2022-09-05 11:02:23
Enter '.help' for usage hints.
sqlite> .schema sharks
CREATE TABLE sharks(id integer NOT NULL, name text NOT NULL, sharktype text NOT NULL, length integer NOT NULL);
sqlite>
Viewing the Structure of a Table
Exploring a Database file
(base) ashish@ashish:~/Desktop/ws/sqlite_db$ sqlite3 sharks.db
SQLite version 3.39.3 2022-09-05 11:02:23
Enter '.help' for usage hints.
sqlite> .tables
sharks
sqlite> select * from sharks;
1|Sammy|Greenland Shark|427
2|Alyoshka|Great White Shark|600
3|Himari|Megaladon|1800
sqlite> ^Z
[3]+ Stopped sqlite3 sharks.db
(base) ashish@ashish:~/Desktop/ws/sqlite_db$ sqlite3 marks.db
SQLite version 3.39.3 2022-09-05 11:02:23
Enter '.help' for usage hints.
sqlite> .tables
marks
sqlite> select * from marks;
2023|8|english|75
2023|8|math|85
2023|8|computer|90
2022|7|english|90
2022|7|math|85
2022|7|computer|95
2023|8|physics|99
2023|8|chemistry|97
2023|8|biology|95
sqlite>
Import a CSV file
(base) ashish@ashish:~/Desktop/ws/sqlite_db$ sqlite3 marks.db SQLite version 3.39.3 2022-09-05 11:02:23 Enter '.help' for usage hints. sqlite> sqlite> .tables sqlite> .mode csv sqlite> .import ./marks.csv marks First line in marks.csv should contain the header with column names. sqlite> .tables
marks
sqlite>
sqlite> select * from marks;
2023,8,english,75
2023,8,math,80
2023,8,computer,90
2022,7,english,90
2022,7,math,85
2022,7,computer,95
sqlite>
Inserting a single row
sqlite> .schema marks
CREATE TABLE IF NOT EXISTS 'marks' ('year' TEXT, 'class' TEXT, 'subject' TEXT, 'marks' TEXT);
sqlite>
sqlite> insert into marks (year, class, subject, marks) values (2023, 8, 'sanskrit', 90);
sqlite> select * from marks;
2023|8|english|75
2023|8|math|80
2023|8|computer|90
2022|7|english|90
2022|7|math|85
2022|7|computer|95
2023|8|sanskrit|90
sqlite>
Inserting multiple rows
sqlite> insert into marks (year, class, subject, marks) values (2023, 8, 'physics', 99), (2023, 8, 'chemistry', '97'), (2023, 8, 'biology', 95);
sqlite> select * from marks;
2023|8|english|75
2023|8|math|80
2023|8|computer|90
2022|7|english|90
2022|7|math|85
2022|7|computer|95
2023|8|sanskrit|90
2023|8|physics|99
2023|8|chemistry|97
2023|8|biology|95
Selection and Filtering
sqlite> select * from marks where marks > 90;
2022|7|computer|95
2023|8|physics|99
2023|8|chemistry|97
2023|8|biology|95
sqlite> select * from marks where class = 8;
2023|8|english|75
2023|8|math|80
2023|8|computer|90
2023|8|sanskrit|90
2023|8|physics|99
2023|8|chemistry|97
2023|8|biology|95
Update
sqlite> select * from marks where class = 8 and subject = 'math';
2023|8|math|80
sqlite>
sqlite> update marks set marks = marks + 5 where class = 8 and subject = 'math';
sqlite> select * from marks where class = 8 and subject = 'math';
2023|8|math|85
Deleting a record
sqlite> select count(*) from marks where subject = 'sanskrit';
1
sqlite> select * from marks where subject = 'sanskrit';
2023|8|sanskrit|90
sqlite> delete from marks where subject = 'sanskrit';
sqlite> select * from marks where subject = 'sanskrit';
sqlite> select count(*) from marks where subject = 'sanskrit';
0
sqlite>
Cursor
|
Row Num |
0:ID |
1:Name |
2:SharkType |
3:Length |
|
0 |
1 |
Sammy |
Greenland Shark |
427 |
|
1 |
2 |
Alyoshka |
Great White Shark |
600 |
|
2 |
3 |
Himari |
Megaladon |
1800 |
|
[0][0] |
[0][1] |
[0][2] |
[0][3] |
|
[1][0] |
[1][1] |
[1][2] |
[1][3] |
|
[2][0] |
[2][1] |
[2][2] |
[2][3] |
A cursor allows us to iterate over a table.
And, a table can be viewed as a list of rows.
And, a row can be viewed as a tuple of cells.
In Code (Part 1)
import sqlite3
conn = sqlite3.connect('sharks.db')
print('Opened database successfully')
cursor = conn.execute('SELECT id, name, sharktype, length FROM sharks')
for row in cursor:
print('ID = ', row[0])
print('NAME = ', row[1])
print('SHARKTYPE = ', row[2])
print('LENGTH = ', row[3])
print('\n')
print('Operation done successfully')
conn.close()
Output
Opened database successfully
ID = 1
NAME = Sammy
SHARKTYPE = Greenland Shark
LENGTH = 427
ID = 2
NAME = Alyoshka
SHARKTYPE = Great White Shark
LENGTH = 600
ID = 3
NAME = Himari
SHARKTYPE = Megaladon
LENGTH = 1800
Operation done successfully
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