Question

I have this SQL statement that works but take a long time to process

I have an a_log table and people table. I need to find the last activity and the associated user for each id for the given person in the people table.

SELECT p.`id`, activity, appphone, appname, dateadd 
FROM people p
LEFT JOIN a_log a
ON p.id = a.id 
WHERE (  dateadd >= '2011/09/13 00:00' and dateadd <= '2011/09/13 23:59') 
AND (a.date_time = (SELECT MAX(a1.date_time)
       FROM activity_log a1
       WHERE a.id = a1.id
       GROUP BY id) OR date_time IS NULL)
    ORDER BY `id` desc limit 0, 100

I have a non unique index on date_time field and id field in the a_log table
I have a primary index on id field and a non unique index on dateadd field in people table

How can i get a shorter execution time on this query?
Thank you

Answer 1

This should work for you:

SELECT p.`id`, p.activity, p.appphone, p.appname, p.dateadd, a.*
FROM people p
LEFT OUTER JOIN
(
    SELECT a.id, a.date_time, a.user  
    FROM activity_log a 
    INNER JOIN 
    (
        SELECT id, MAX(date_time) as date_time
                    FROM activity_log 
                    GROUP BY id
    ) a1  ON a.id = a1.id and a.date_time = a1.date_time
) a ON p.id = a.id 
WHERE (  dateadd >= '2011/09/13 00:00' and dateadd <= '2011/09/13 23:59'   and `agent_or_underwriter` != 'agent') 
ORDER BY p.id desc limit 0, 100