Left join to get most recent entries - mysql

Question

I have the tables users and statuses . I want to select all the users, plus any statuses they might have, but only the most recent status from each user.
Here is the code that doesn't work:
SELECT users.id, alias, gender, login, logout, users.create_date, statustext as statustxt, TIMESTAMPDIFF(YEAR,birthdate,CURDATE()) AS age
FROM users
LEFT JOIN statuses s ON users.id = s.user_id
WHERE s.ID = (
SELECT MAX(s2.ID)
FROM statuses s2
WHERE s2.user_id = s.user_id
)
This gets the users with the most recent statuses, but not the users from the users table as well. Maybe it can be fixed by some small adjustment?
I got the sub query by searching, but I don't understand how that code works. It seems to compare two versions of the same table (For example: WHERE s2.user_id = s.user_id ) . Where can I read about this sort of technique?
Is a sub query required in this case by the way?
If you can find a solution would be great, and some basic explanation of how it works would highly appreciated.
----------EDIT---------------
I took one of the responses (by maresa) and combined with the sub query of my initial code , and this works(!) It has 3 selects and looks a bit over complicated maybe?:
SELECT users.id, alias, gender, login, logout, users.create_date, statustext as statustxt, TIMESTAMPDIFF(YEAR,birthdate,CURDATE()) AS age
FROM users
LEFT JOIN (
SELECT user_id, statustext FROM statuses s
WHERE s.ID = (
SELECT MAX(s2.ID)
FROM statuses s2
WHERE s2.user_id = s.user_id
)
) as s ON users.id = s.user_id

Answer 1

I've encountered similar problem. This post is relevant: http://www.microshell.com/database/sql/optimizing-sql-that-selects-the-maxminetc-from-a-group/.
Regarding your specific query, since you care only the latest status, you want to first get the latest status from each users. Assuming that the latest status has the latest id (based on your sample), the SQL would be below:
SELECT
MAX(ID), statustext, user_id
FROM
statuses
GROUP BY
user_id
What the above query does is, to get the latest status per user_id. Once you get that, you can think of it as if it's a table. Then simply join on this "table" (the query) instead of the real one (statuses table). Therefore, your query would be like below:
SELECT
users.id, alias, gender, login, logout, users.create_date, statustext as statustxt, TIMESTAMPDIFF(YEAR,birthdate,CURDATE()) AS age
FROM
users
LEFT JOIN (
SELECT
MAX(ID), user_id
FROM
statuses
GROUP BY
user_id
) as s ON users.id = s.user_id
LEFT JOIN statuses ON statuses.ID = s.ID -- EDIT: Added this line.

Answer 2

You might use a subselect as the join, and limit to show only 1 row:
SELECT
users.id,
alias,
gender,
login,
logout,
users.create_date,
statustext as statustxt,
TIMESTAMPDIFF(YEAR,birthdate,CURDATE()) AS age
FROM users
LEFT JOIN (
SELECT user_id,statustext
FROM statuses s1
WHERE s1.user_id = users.id
ORDER BY status_date DESC
LIMIT 1
) s ON users.id = s.user_id

Answer 3

You could use a in clause with a tuple
SELECT
users.id
, alias
, gender
, login
, logout
, users.create_date
, statustext as statustxt
, TIMESTAMPDIFF(YEAR,birthdate,CURDATE()) AS age
FROM users
LEFT JOIN statuses s ON users.id = s.user_id
WHERE (s.user_id, s.ID) in (
SELECT user_id, MAX(s2.ID)
FROM statuses s2
group by user_id
)