使用最新条目从两个表输出数据

Question

I have done a good search for a similar question, but with no joy. I think the answer to my question is based around DISTINCT, GROUP and UNION, but just can't put the together in any way which makes sense.

I have 2 tables:

users(id, username)
activitylog(id, userid, usernamedisp, activity)

Sample data:

users 
id, username
 1, Joe Bloggs
 2, Jane Doe
 3, John Smith

activitylog
id, userid, usernamedisp, activity
 1,      3, John Smith  , logged in
 2,      3, John Smith  , visited about us page
 3,      1, Joe Bloggs  , logged in
 4,      3, John Smith  , logged out
 5,      2, Jane Doe    , logged in
 6,      1, Joe Bloggs  , logged out
 7,      2, Jane Doe    , visited about us page

(there is another unrelated but valid reason why the user's name appears in both tables)

I want the output to list the users in order of users.id along with activitylog.username and finally only the most recent activitylog.activity, which should look as follows:

User, Username  , Last Activity 
   1, Joe Bloggs, logged out 
   2, Jane Doe  , visited about us page
   3, John Smith, logged out

While I could do this by running a query inside a loop on each result (SELECT activity from activitylog where userid = $foo ORDER BY id DESC, LIMIT 0,1) - I would rather run it all off in one nice clean piece of code as the number of users could be between 50-100 and that's too many queries for my comfort.

I'm sure this is possible, but I just can't seem to put it together.

Answer 1

YOu need a two-part query: one to get the list of usersIDs and their "max" id, which would be their latest activity. Then a container query which takes those IDs and fetches the rest of the information:

SELECT activitylog.userid, users.username, activitylog.activity
FROM activitylog
LEFT JOIN users ON activitylog.userid = users.id
WHERE activitylog.id IN (
   SELECT MAX(id)
   FROM activitylog
   GROUP BY userid
)

Answer 2

Contd. from discussion in comments...

This query should get you the next solution set you are looking for.

SELECT AL.userid
    ,users.username
    ,AL.activity
FROM users
LEFT JOIN (
    SELECT activitylog.userid
        ,activitylog.activity
    FROM activitylog
    WHERE activitylog.id IN (
            SELECT MAX(id)
            FROM activitylog
            GROUP BY userid
            )
    ) as AL ON AL.userid = users.id