Question

Two simple tables

Base table

+--------+
|id|value|
+--------+
|  |     |
+--------+

Event table (with a lot of data..)

+--------------+
|id|event| date|
+--------------+
|  |     |     |
+--------------+

Then I would like to have a list of all base.value with corresponding to their last events (including values without event entries)

+----------------+
|id|lastEvt|value|
+----------------+
|  |       |     |
+----------------+

This is a (working but) very slow attempt

SELECT *
  FROM  ( 
    SELECT base.id,
           event.event,
           base.value
      FROM base
           LEFT OUTER JOIN event
                        ON base.id = event.id
     ORDER BY event.date DESC
) 
AS res
 GROUP BY res.id;

I suspect there is a better/faster way of doing the query, but I don’t know how..

Answer 1

SELECT b.id, b.value, e.event
    FROM base b
        LEFT JOIN (SELECT id, MAX(date) AS LastEventDate
                       FROM event
                       GROUP BY id) q
            INNER JOIN event e
                ON q.id = e.id
                    AND q.LastEventDate = e.date
            ON b.id = q.id