Understanding the READ COMMITTED Isolation Level in SQL

Demonstrate Isolation Level READ COMMITTED

Write a SQL query to demonstrate the READ COMMITTED isolation level.

Solution:

-- Set the isolation level to READ COMMITTED.
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
BEGIN TRANSACTION; -- Begin the transaction.
-- Read data from the Employees table.
SELECT * FROM Employees WHERE EmployeeID = 1;
-- Simulate another transaction modifying the same data.
UPDATE Employees SET Salary = 55000 WHERE EmployeeID = 1;
COMMIT TRANSACTION; -- Commit the transaction.

Explanation:

1. Purpose of the Query :

1. The goal is to demonstrate how the READ COMMITTED isolation level ensures that only committed data is visible to other transactions.

2. Key Components :

1. SET TRANSACTION ISOLATION LEVEL READ COMMITTED : Sets the isolation level.
2. SELECT and UPDATE : Demonstrates reading and modifying data within the transaction.

3. Why Use READ COMMITTED? :

1. This isolation level prevents dirty reads, ensuring that uncommitted changes are not visible to other transactions.

4. Real-World Application :

1. For example, in a banking system, you might use this isolation level to ensure that account balances are only updated after a transaction is committed.

Additional Notes:

• The READ COMMITTED isolation level is the default in many database systems.
• Scenarios where READ COMMITTED is appropriate include:
• Preventing dirty reads in multi-user environments.
• Ensuring that queries only see committed data.
• Important Considerations :
• While READ COMMITTED prevents dirty reads, it does not prevent non-repeatable reads or phantom reads.

For more Practice: Solve these Related Problems:

• Write a SQL query to demonstrate how the READ COMMITTED isolation level prevents dirty reads in a multi-user environment.
• Write a SQL query to simulate two concurrent transactions where one reads data while the other modifies it under the READ COMMITTED isolation level.
• Write a SQL query to test whether uncommitted changes are visible to other transactions when using the READ COMMITTED isolation level.
• Write a SQL query to observe the behavior of the READ COMMITTED isolation level when reading data that is being updated by another transaction.

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