Question

Say I have a ‘user_log’ table with the following field:

• id
• user_id
• status_text
• timestamp

How do I write a query that selects only the last update for all the users in that table?

Appreciate your help 🙂

Answer 1

Assuming ID is an auto-increment id, you can do this:

SELECT * 
FROM user_log 
INNER JOIN 
(SELECT MAX(id) as id FROM user_log GROUP BY user_id) last_updates 
ON last_updates.id = user_log.id

If you want to be really pedantically correct and cover all the corner cases (multiple updates with the same timestamp, out-of-order insertions, etc) you can use the timestamp:

SELECT * 
FROM user_log
INNER JOIN
(SELECT MAX(id)
 FROM user_log 
 INNER JOIN 
 (SELECT DISTINCT user_id, MAX(timestamp) as timestamp 
  FROM user_log GROUP BY user_id
 ) last_updates 
 ON last_updates.user_id = user_log.user_id 
    AND last_updates.timestamp = user_log.timestamp
) last_update
ON last_update.id = user_log.id