How to only get DISTINCT rows from a JOIN query: MySQL

Question

Two tables. Table one is users. Table two is user events. One user has many events. I just want to get a list of the users with the most recent events. I can obviously set it to select more rows than I need and filter out the duplicates but I really want to just select the exact number of rows I need in the SQL.

This SQL query gives duplicates of a.name where one user has had more than one event recently. I thought that DISTINCT would prevent duplicates. What am I doing wrong? How do I just get one row for each user?

SELECT DISTINCT (a.name), b.date , a.id
FROM `users` a
INNER JOIN events b
ON a.id = b.userid 
WHERE now() > b.date 
ORDER BY b.date DESC, a.id DESC
LIMIT 30;

Table users...

id name

Table events...

id userid date

I don't need to select the b.date value but this is needed for DISTINCT to work because it is in the ORDER BY part, I believe.

Answer 1

You could GROUP BY the user and only take the maximum date (or the minimum, if you want the oldest of the events).

SELECT a.name,
       max(b.date) date,
       a.id
       FROM users a
            INNER JOIN events b
                       ON a.id = b.userid 
       WHERE now() > b.date 
       GROUP BY a.id,
                a.name
       ORDER BY max(b.date) DESC,
                a.id DESC
       LIMIT 30;

DISTINCT won't help you, when there are different date values for a user. Those records are distinct because of the different date values, though sharing a user.