Difference between SQL Commit and SQL Rollback

Introduction

Data transaction management is an important skill to have when working with databases. Tools like structured query language (SQL) helps you do this efficiently. It offers a number of built-in commands that can handle transactions, ensuring data integrity and consistency. The two most commonly used commands in this context are COMMIT and ROLLBACK. In this article, we will try to understand the differences between the COMMIT and ROLLBACK commands in SQL, as we learn them in detail. We will also explore their usage through practical examples to master transaction management in SQL.

If you are just starting to explore SQL, here is a beginner's guide to help you: SQL for Data Science: A Beginner's Guide

General description

• Understand the concept of transactions in SQL.
• Learn what the COMMIT and ROLLBACK commands do in SQL.
• Learn the key differences between the COMMIT and ROLLBACK commands.
• Learn how to practically use these commands in SQL.

What is a transaction in SQL?

In SQL, a transaction is a sequence of one or more operations treated as a single unit of work. In other words, it is a set or combination of commands or actions (such as INSERT, UPDATE, DELETE, etc.) that together form a process. The point to note here is that if even one of these commands is not completed, the entire process will be aborted. Therefore, all the operations must be completed for the transaction to take place.

Transactions follow the following properties, collectively referred to as ACID:

• Atomicity: They ensure that all operations within the transaction are completed, if not, the transaction is cancelled.
• Consistency: They ensure that the database remains in a valid state before and after the transaction.
• Isolation: They ensure that simultaneous transactions do not interfere with each other.
• Durability: They ensure that once a transaction is confirmed, it is permanently applied to the database.

SQL COMMIT Command

The COMMIT command in SQL is used to save all the changes made during the current transaction. Once a COMMIT command is issued, the changes become permanent and visible to other users.

Syntax: COMMIT;

Key points

• The COMMIT command ends the transaction, making all changes made by the transaction permanent.
• The COMMIT operation is irreversible.
• Once executed, the changes will be visible to other users and sessions.

Practical example

START TRANSACTION;

INSERT INTO employees (name, position, salary) VALUES ('Alice', 'Engineer', 70000);
UPDATE employees SET salary = salary + 5000 WHERE name="Alice";

COMMIT;

In this example, the transaction inserts a new employee and updates the salary. The COMMIT command saves these changes.

SQL ROLLBACK Command

The ROLLBACK command in SQL is used to undo all the changes made during the current transaction. You can use it if an error occurs during a transaction or if you change your mind about the operations performed. It reverts the database to its state before the transaction was started.

Syntax: ROLLBACK;

Key points

• He BACK The command reverts all changes made by the current transaction.
• Restores the database to the state it was in before the transaction was started.
• It is very useful for handling errors and maintaining data integrity.
• Some database systems support partial rollbacks to a recovery point. This allows only part of a transaction to be rolled back.

Practical example

START TRANSACTION;

INSERT INTO employees (name, position, salary) VALUES ('Bob', 'Manager', 90000);
UPDATE employees SET salary = salary + 5000 WHERE name="Bob";

ROLLBACK;

In this case, the transaction inserts a new employee and updates the salary. However, the ROLLBACK command reverses these changes.

Differences between COMMIT and ROLLBACK in SQL

Conclusion

Understanding and using the COMMIT and ROLLBACK commands effectively is essential for managing transactions in SQL. By using COMMIT, you make changes permanent and visible to others. Meanwhile, ROLLBACK allows you to undo changes and revert the database to its previous state. Together, these commands help maintain data integrity, handle errors, and ensure that the database remains in a consistent state. Whether you are developing a new application or managing an existing database, mastering COMMIT and ROLLBACK will help you maintain control over your data and ensure that your transactions execute correctly.

Learn more: SQL: A Complete Guide from Basics to Advanced Level

Frequent questions