How can you ensure data integrity using transactions?

3 How do you use transactions in SQL?

To use transactions in SQL, you need to use the following commands: BEGIN, COMMIT, and ROLLBACK. BEGIN starts a new transaction and marks the point where the changes to the database will be saved or discarded. COMMIT ends a transaction and saves the changes to the database permanently. ROLLBACK ends a transaction and discards the changes to the database, restoring it to the state before the transaction began. For example, to transfer money from one account to another, you can use the following SQL statements:

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;        

This transaction will atomically update the balances of both accounts and commit the changes to the database. If any error occurs during the transaction, you can use ROLLBACK to cancel the transaction and undo the changes.

4 What are the types of transactions?

Transactions can be classified into different types based on their level of isolation, which determines how they interact with other concurrent transactions. The higher the level of isolation, the more data integrity is preserved, but the lower the concurrency and performance are. Conversely, the lower the level of isolation, the more concurrency and performance are improved, yet the more data integrity is compromised. The four levels of isolation are serializable, repeatable read, read committed, and read uncommitted. Serializable offers the highest level of isolation, preventing all types of data anomalies; however, it also reduces concurrency and performance. Repeatable read provides a high level of isolation, preventing dirty reads and non-repeatable reads; yet it allows phantom reads. Read committed offers a medium level of isolation, preventing dirty reads; but allowing non-repeatable reads and phantom reads. Lastly, read uncommitted is the lowest level of isolation, allowing dirty reads, non-repeatable reads, and phantom reads; yet improving concurrency and performance.

5 How do you choose the level of isolation for transactions?

The level of isolation for transactions depends on the trade-off between data integrity and performance that you want to achieve for your database. The default level of isolation for most database systems is read committed, which offers a reasonable balance between data integrity and performance. However, you may need to adjust the level of isolation according to the requirements and characteristics of your application and data. For example, if your application involves financial transactions or sensitive data, you may want to use serializable or repeatable read to ensure the highest data integrity. On the other hand, if your application involves analytical queries or low-risk data, you may want to use read uncommitted or read committed to improve the performance and concurrency.