SQL transactions are fundamental to maintaining data integrity in database operations. They ensure that a series of SQL statements are executed as a single unit of work, either completing successfully or rolling back entirely if an error occurs.
A transaction is a sequence of one or more SQL operations that are treated as a single, indivisible unit. It's an all-or-nothing proposition: either all the operations within the transaction succeed, or none of them do.
Transactions adhere to the ACID Properties, which stand for:
This command marks the start of a transaction.
BEGIN TRANSACTION;
COMMIT saves all the changes made during the transaction.
COMMIT;
ROLLBACK undoes all changes made during the transaction.
ROLLBACK;
Here's a simple example of a transaction that transfers money between two accounts:
BEGIN TRANSACTION;
UPDATE accounts SET balance = balance - 100 WHERE account_id = 1;
UPDATE accounts SET balance = balance + 100 WHERE account_id = 2;
IF @@ERROR = 0
COMMIT;
ELSE
ROLLBACK;
In this example, if both UPDATE statements succeed, the transaction is committed. If an error occurs, the entire transaction is rolled back, ensuring the database remains in a consistent state.
As you become more comfortable with basic transactions, you may want to explore advanced concepts such as:
Understanding and properly implementing SQL transactions is crucial for maintaining data integrity in your database applications. They form the backbone of reliable data management systems and are essential for any serious database developer.