Difference Between SQL Commit and SQL Rollback

Introduction

Managing data transactions is an important skill to have while working with databases. Tools like Structured Query Language (SQL) help you do this efficiently. It offers an array of built-in commands that can handle transactions, ensuring data integrity and consistency. 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 about them in detail. We will also explore their usage through practical examples to master transaction management in SQL.

If you’re just starting out to explore SQL, here’s a beginner’s guide to help you: SQL For Data Science: A Beginner Guide

Overview

• Understand the concept of transactions in SQL.
• Learn what the COMMIT and ROLLBACK commands do in SQL. 
• Know the key differences between 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’s 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 canceled. Hence, all the operations must be completed for the transaction to be done.

Transactions follow the below properties, collectively termed as ACID:

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

SQL COMMIT Command

The COMMIT command in SQL is used to save all 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 finalizes 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 this if an error occurs during a transaction, or if you change your mind about the operations performed. It reverts the database to its previous state before the transaction began.

Syntax: ROLLBACK;

Key Points

• The ROLLBACK command reverses all changes made by the current transaction.
• It restores the database to the state it was in before the transaction started.
• It’s very handy for handling errors and maintaining data integrity.
• Some database systems support partial rollbacks to a savepoint. This allows you to roll back only part of a transaction.

Practical Example

START TRANSACTION;

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

ROLLBACK;

Here, the transaction inserts a new employee and updates the salary. However, the ROLLBACK command reverts these changes.

Differences Between COMMIT and ROLLBACK in SQL

Conclusion

Understanding and using COMMIT and ROLLBACK commands effectively are essential for managing transactions in SQL. By using COMMIT, you make your 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 are executed correctly.

Learn More: SQL: A Full Fledged Guide from Basics to Advanced Level

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