What are the main commands used for transaction control in a relational database?

The following are the main SQL commands used to control transactions in relational databases:

• BEGIN or START TRANSACTION — starts a new transaction.
• COMMIT — saves all changes made within the transaction.
• ROLLBACK — reverts all changes made since the transaction started.

Example of usage in Python with the sqlite3 library:

import sqlite3

conn = sqlite3.connect('example.db')
cursor = conn.cursor()

try:
    conn.execute('BEGIN')
    cursor.execute("INSERT INTO users(name) VALUES ('Alice')")
    cursor.execute("INSERT INTO users(name) VALUES ('Bob')")
    conn.commit()  # save changes
except Exception:
    conn.rollback()  # revert changes on error
finally:
    conn.close()

These commands help manage data integrity and ensure atomicity of operations.