In Python you can connect to a SQLite file by using the sqlite3 module.

import sqlite3
con = sqlite3.connect('example.db')

Using the cursor instance you can execute SQL queries in Python.

c = con.cursor()
c.execute("SELECT * FROM clients")

You can fetch results using e.g. the fetchall() method provided by the Cursor instance.

# fetching results
results = cursor.fetchall()

# outputting results row by row
for row in results:
    print(row)

# close database connection after performing operations
con.close()

In this way you can join data from two database tables using sqlite3 in Python. In the example provided below customer order data is joined with client data when client_id column entries match.

# define SQLite query in Python
query = '''
SELECT *
FROM orders
JOIN clients
ON orders.customer_id = clients.customer_id
'''

# execute SQLite query in Python
c.execute(query)