Transaction Control Commands (TCC) in a Database Management System (DBMS) are used to manage and control changes made during transactions. A transaction refers to a single logical unit of work that may consist of one or more SQL operations, such as insertions, updates, or deletions. Transaction control ensures that all operations within a transaction are completed successfully before being permanently applied to the database. If any operation fails, the database can revert to its previous consistent state. The main commands used for transaction control are COMMIT and ROLLBACK. These commands maintain data integrity, consistency, and reliability, especially in multi-user environments, by managing how and when changes become permanent or are undone within the database system.
1. COMMIT Command
The COMMIT command is used to permanently save all changes made during the current transaction in the database. Once a COMMIT is executed, the changes become visible to all users and cannot be undone. For example, after inserting or updating data, using COMMIT; ensures those modifications are finalized. This command marks the successful completion of a transaction, confirming that all related operations have been executed without error. In multi-user environments, COMMIT helps maintain consistency by making sure all participants see the updated data. It is often used after critical operations like financial transactions or record updates to ensure data durability, reliability, and integrity across the database.
2. ROLLBACK Command
The ROLLBACK command is used to undo changes made during the current transaction before they are committed. It restores the database to its last consistent state, ensuring that no partial or incorrect data is saved. For example, if a transaction involves multiple updates and one fails, executing ROLLBACK; cancels all operations in that transaction. This command is essential for maintaining data accuracy and consistency when errors, system failures, or incorrect inputs occur. In multi-user databases, ROLLBACK prevents faulty or incomplete transactions from affecting shared data. It provides a safety mechanism, allowing administrators and users to correct mistakes without permanently altering the database.