Retrieve Up-to-Date Data with READ COMMITTED

Read Latest Committed Data in READ COMMITTED Mode

Write a PostgreSQL query to illustrate how a transaction operating in READ COMMITTED isolation level reads the latest committed data.

Solution:

-- Begin a transaction with READ COMMITTED isolation.
BEGIN;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

-- Select current orders to see the latest committed data.
SELECT * FROM Orders;

-- Commit the transaction.
COMMIT;

Explanation:

• Purpose of the Query:
• The goal is to demonstrate that a transaction in READ COMMITTED mode sees the most recent committed changes.
• This highlights the dynamic nature of data visibility under READ COMMITTED.
• Key Components:
• SELECT * FROM Orders; : Retrieves the current state of the Orders table.
• Real-World Application:
• Frequently used in transactional systems where up-to-date information is required for processing orders.

Notes:

• READ COMMITTED isolation ensures that each query within the transaction sees data committed before its execution.
• It may result in non-repeatable reads if data changes between queries.

For more Practice: Solve these Related Problems:

• Write a PostgreSQL query to begin a transaction with READ COMMITTED isolation and select the latest transactions from the Transactions table.
• Write a PostgreSQL query to start a transaction with READ COMMITTED isolation and retrieve the most recent updates from the Users table.
• Write a PostgreSQL query to begin a transaction with READ COMMITTED isolation and select the latest log entries from the Logs table.
• Write a PostgreSQL query to start a transaction with READ COMMITTED isolation and fetch the current state of the Sessions table.

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous PostgreSQL Exercise: Begin Transaction with Custom Isolation Level for Multiple Operations.
Next PostgreSQL Exercise: Consistent Snapshot in REPEATABLE READ Mode.