Question

I have the following query that I need to convert to rails like syntax. Is there any way to do it or is it better to just use plain MYSQL for this?

SELECT `terminals`.`serial`, Count(*) AS count, MAX(`logs`.`created_at`) AS created_at 
FROM 
(SELECT * FROM `terminals` WHERE `terminals`.`user_id`= 1) AS terminals 
INNER JOIN `bap-backend`.`logs` ON terminals.`serial`=`logs`.`serial` 
GROUP BY `serial` ORDER BY `logs`.`created_at`

The inner Select is to make sure only terminals of the current_user get selected, then I only need the terminals serial. I need this query to give an overview of all the user his terminals and display how many logs the terminal has provided and when the last log occured. The query works on my test data only the implementation in rails is a bit complicated for me.

Thanks!

EDIT

For the google people, just use find_by_sql, you can still add variables in it. Just add a class before the command, like following example:

@items_event = Item.find_by_sql(["SELECT items.*, ei_relationships.itemprice, ei_relationships.currency, ei_relationships.itemunit
                                      FROM `ei_relationships` INNER JOIN `items` ON `items`.`id` = `ei_relationships`.`item_id`
                                      WHERE `ei_relationships`.`event_id` = ?", @event[:id]])

Answer 1

I don’t claim to know anything about rails, so I can’t answer that part of the question. But if you do stick with plain MySQL, your query could be cleaned up a little:

SELECT
    terminals.serial,
    COUNT(*) AS count,
    MAX(logs.created_at) AS created_at 
FROM 
    terminals 
    INNER JOIN `bap-backend`.logs
        ON terminals.serial = logs.serial AND terminals.user_id = 1 /* instead of performing a subquery, just add this to your join conditions */
GROUP BY
    serial
ORDER BY
    logs.created_at

This takes out one subquery, which should help your performance.