Difference Between COMMIT and ROLLBACK in SQL
Last Updated : 19 Dec, 2024
In SQL, transaction control is essential for managing changes in a database effectively. COMMIT and ROLLBACK are two crucial Transaction Control Language (TCL) commands that help maintain data integrity and consistency. While COMMIT ensures that all changes in a transaction are permanently saved, ROLLBACK provides a mechanism to undo changes when something goes wrong.
Understanding the differences between these commands is critical for database administrators, developers, and anyone working with transactional data to ensure reliable and error-free database operations. Proper usage of these commands ensures reliable and error-free database operations while maintaining data stability.
Difference Between COMMIT and ROLLBACK
The table below highlights the key differences between COMMIT and ROLLBACK in SQL:
| Feature | COMMIT | ROLLBACK |
| Function | Permanently saves changes made by the current transaction. | Undoes changes made by the current transaction. |
| Undo Capability | Cannot undo changes after execution. | Reverts the database to its previous state before the transaction. |
| When Applied | Used when the transaction is successfully completed. | Used when the transaction fails, is incorrect, or aborted. |
| Data Integrity | Ensures that changes are saved permanently. | Ensures that errors do not affect the database by undoing partial changes. |
| Syntax | COMMIT; | ROLLBACK; |
| Error Handling | No changes are rolled back even if errors occur after the COMMIT statement. | Automatically undoes uncommitted changes in case of errors or failures. |
Understanding COMMIT and ROLLBACK with Examples
A sample table is created to demonstrate how COMMIT and ROLLBACK work. This table will be used for all examples to maintain consistency. Consider the following STAFF table with records:
STAFF Table:
1.COMMIT
COMMIT in SQL is a transaction control language that is used to permanently save all changes made during the current transaction. After executing a COMMIT statement, the changes are irreversible, and the database cannot revert to its previous state. The COMMIT command ensures that the changes made during the transaction are reflected in the database.
Syntax:
COMMIT;
Example:
In the following example, we will demonstrate how to use the COMMIT command to permanently save changes to a table. This ensures that any modifications made to the data are saved and cannot be undone. Select records where Allowance equals 400.
Query:
SELECT *
FROM Staff
WHERE Allowance = 400;
sql> COMMIT;
Output:
Explanation:
- The
UPDATE statement modifies the Allowance value for employees with an initial value of 400. - After executing the COMMIT statement, any changes made during the transaction are saved permanently.
2. ROLLBACK
ROLLBACK in SQL is a transactional control language that is used to undo changes made during the current transaction that have not yet been committed. This command is particularly useful when errors occur, or the transaction is aborted. The ROLLBACK command ensures that the database returns to its previous state by undoing uncommitted changes.
Syntax:
ROLLBACK;
Example:
In this example, we will use the ROLLBACK command to demonstrate how to revert changes to a table. This ensures that any errors or unintended modifications are undone, restoring the database to its previous state. Update Allowance for employees with an Allowance of 300.
Query:
SELECT *
FROM EMPLOYEES
WHERE ALLOWANCE = 400;
ROLLBACK;
Output:
Explanation:
- The
UPDATE statement modifies the Allowance value for employees with an initial value of 300 - The ROLLBACK statement undoes all uncommitted changes, restoring the
Staff table to its state before the transaction.
When to Use COMMIT and ROLLBACK
- Use COMMIT when all operations in a transaction are successful and we want to save changes permanently.
- Use ROLLBACK when an error occurs, or the transaction needs to be aborted, ensuring the database remains unaffected by partial or incorrect updates.
Conclusion
Understanding the roles of COMMIT and ROLLBACK is essential for effective transaction management in SQL. Use COMMIT to save changes permanently after a successful transaction and ROLLBACK to revert changes in case of errors. By applying these commands correctly, we can maintain the stability and integrity of our database. Mastering these commands allows developers and administrators to confidently handle complex transactional workflows and prevent data corruption.
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