ACID properties in SQL transactions refer to a set of principles that ensure reliable processing of database transactions. ACID stands for Atomicity, Consistency, Isolation, and Durability. Each of these properties plays a crucial role in ensuring data integrity and reliability during the execution of transactions. By adhering to these principles, databases can effectively manage transactions in a way that prevents data corruption and maintains accurate records.
Atomicity guarantees that a transaction is treated as a single unit of work. This means that all the operations within the transaction must complete successfully; if any part of the transaction fails, the entire transaction is rolled back. For example, consider a banking application where funds are being transferred from one account to another. If the debit from one account succeeds but the credit to the other account fails, atomicity ensures that neither account is changed, preventing any incorrect balance.
Consistency ensures that a transaction takes the database from one valid state to another, maintaining all defined rules, such as data integrity constraints. In the earlier banking example, the total amount of money in the system before and after the transaction should remain the same. If a transaction violates data integrity rules, the transaction would not be allowed to complete, keeping the database consistent. Isolation ensures that concurrent transactions do not interfere with each other, meaning the result of a transaction should not be visible to others until it is complete. Lastly, Durability guarantees that once a transaction is committed, its results are permanent, even in the event of a system crash. For example, if a transaction that adds a new user is completed and the system crashes afterward, the new user should still be present once the system is restored. Together, these ACID properties create a strong foundation for reliable database transaction management.