The transaction isolation level determines how concurrent database transactions are isolated from each other. It defines the visibility and behavior of changes made by one transaction to other transactions.

In SQL CLI, you can control the transaction isolation level using the SET TRANSACTION ISOLATION LEVEL statement. Let’s explore the different isolation levels and how to set them.

Types of Transaction Isolation Levels

1. READ UNCOMMITTED: This is the lowest isolation level where a transaction can see uncommitted changes made by other transactions.

2. READ COMMITTED: This level allows a transaction to see only committed changes made by other transactions.

3. REPEATABLE READ: In this isolation level, a transaction sees only committed changes and prevents non-repeatable reads, but it can still encounter phantom reads.

4. SERIALIZABLE: This is the highest isolation level, providing strict data integrity by preventing concurrent transactions from reading or modifying the same data.

Setting Transaction Isolation Levels in SQL CLI

To set the transaction isolation level in SQL CLI, follow these steps:

1. Open your SQL CLI client and connect to the database.

2. Execute the following command to set the desired isolation level:

SET TRANSACTION ISOLATION LEVEL <isolation_level>;

Replace <isolation_level> with the desired level (e.g., READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE).

1. Confirm that the isolation level is set correctly by executing the following command:

SELECT @@TRANCOUNT AS 'Transaction Isolation Level';

It will display the current transaction isolation level.

Example:

Let’s say you want to set the transaction isolation level to READ COMMITTED. Here’s how you can do it in SQL CLI:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
SELECT @@TRANCOUNT AS 'Transaction Isolation Level';

The output will show the current transaction isolation level set as READ COMMITTED.

Conclusion

Controlling transaction isolation levels in SQL CLI allows you to manage the concurrency and data integrity of your database transactions. By setting the appropriate isolation level, you can control how changes made by one transaction are visible to other concurrent transactions. Understanding and selecting the right isolation level is crucial to ensure the reliability and consistency of your database operations.

References:

• Microsoft Documentation: SET TRANSACTION ISOLATION LEVEL

• PostgreSQL Documentation: Transaction Isolation in SQL CLI

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