How to Retrieve the Most Recent Message from Each User Group in SQL?

How to Retrieve the Latest Message from Each User's Group Using GROUP BY

In your database, you have a table named "messages" containing the following columns:

• id
• from_id
• to_id
• subject
• message
• timestamp

Your goal is to extract the latest message from each user's group. For instance, this is similar to the message list you see in your Facebook inbox before clicking on a specific conversation.

Initially, you tried using the following query, which groups messages by the from_id column:

SELECT * FROM messages GROUP BY from_id

However, you noticed that this query returns the oldest message instead of the latest.

To overcome this limitation, you need to determine the latest timestamp values for each message group using a subquery. Then, join this subquery with the main "messages" table to filter out only the latest messages:

SELECT t1.* 
FROM messages t1
JOIN (
    SELECT from_id, MAX(timestamp) timestamp 
    FROM messages 
    GROUP BY from_id
) t2 ON t1.from_id = t2.from_id AND t1.timestamp = t2.timestamp;

This modified query effectively identifies the latest records in each group, providing you with the desired results.

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