Question

I’m breaking my head trying to modify this query(thx sgeddes) in order to
get at result not only from db_events.events fields, instead join it with some db_system.devices fields

SELECT e.* 
FROM db_events.events e 
   JOIN (
      SELECT Max(id) MaxId, device_id
      FROM db_events.events
      GROUP BY device_id ) e2 on e.Id = e2.MaxId AND e.device_id = e2.device_id
WHERE e.device_id IN (
            SELECT device_id 
            FROM db_system.devices 
            WHERE vendor = 1)
ORDER BY e.id DESC

How can I get it without repeat the subquery:

            SELECT * 
            FROM db_system.devices 
            WHERE vendor = 1

I need get db_system.devices.brand and db_system.devices.model joined with final results, and
I tried to modify it step to step, I tried with temporary tables, I suspect it should be something simple, but I have not been able to do it, of course thank you very much…

Answer 1

is this what you want?

SELECT  e.*, a.* 
FROM    db_events.events e 
        INNER JOIN 
        (
            SELECT Max(id) MaxId, device_id
            FROM db_events.events
            GROUP BY device_id 
        ) e2 on e.Id = e2.MaxId AND 
                e.device_id = e2.device_id
        INNER JOIN db_system.devices a
            ON e.device_id = a.device_id  AND 
                a.vendor = 1
ORDER   BY e.id DESC

the condition a.vendor = 1 can also be moved on WHERE clause and the result is still the same since you are using INNER JOIN

SELECT ....
FROM   .... JOIN ....
WHERE  a.vendor = 1
ORDER  BY ...