Get relative data with max in mysql - mysql

Question

I have a table called log_payment that has a series of payment records like:
log_user_id, log_date, log_payment_id
13, 2013-01-01 01:13:00, TRIAL<BR>
13, 2013-01-02 01:18:00, 1<BR>
13, 2013-01-03 01:05:00, 2
What I want to get is the payment id and date of the users last record. So I want that user_id's last transaction was 01/03 and has a payment id of 2. So I wrote this query:
select max(log_date) as max_date,log_user_id,log_payment_id from log_payment group by log_user_id
but it returns 13, 2013-01-03 01:05:00, TRIAL
So based on some data I found somewhere else, I tried this:
select log_user_id, max_date, log_payment_id from (select log_user_id,max(log_date) as max_date from log_payment group by _log_user_id) payment_table inner join log_payment on payment_table.log_user_id = log_payment.log_user_id and payment_table.max_date = log_payment.log_date
But this goes on for several minutes until I finally just cancel it. What am I missing?

Answer 1

Your query, which I have reparsed, looks good, except for the _log_user_id in the group by. It should be log_user_id:
select log_user_id,
max_date,
log_payment_id from
(select log_user_id,max(log_date) as max_date from log_payment group by _log_user_id)
payment_table
inner join
log_payment
on payment_table.log_user_id = log_payment.log_user_id and
payment_table.max_date = log_payment.log_date
Depending on the size of your tables the query might be slow. Try adding a LIMIT 10 at the end of the query to see if that gets you the desired result for the first 10 tuples.
--dmg

Answer 2

The best solution for the Group by order is use a subquery to make the order by for you:
SELECT t1.*
FROM `log_payment` t1
WHERE `id` = (
SELECT `id`
FROM `log_payment` `t2`
WHERE `t2`.`log_user_id` = `t1`.`log_user_id`
ORDER BY `t2`.`log_date` DESC
LIMIT 1
)
It also should be really fast. Of course it always relies on your index's setup.