MySql : left join users table with transactions table return several rows

Question

• I have 2 tables : users and paypal_transactions
• For each user, we have an id (named user_id in paypal_transactions table)
• A user may have several paypal_transactions. Relation one to many
• I need to grab the latest transaction id (ordered by date_dt DESC) when I do my query

My current query :

SELECT `Transaction`.*, `User`.*, `Tipster`.`username`
FROM `pronostics_framework`.`users` AS `User`
LEFT JOIN `pronostics_framework`.`users` AS `Tipster` ON (`User`.`tipster_id` = `Tipster`.`id`)
LEFT JOIN `pronostics_framework`.`paypal_transactions` AS `Transaction` ON (`User`.`id` = `Transaction`.`user_id`)
ORDER BY `User`.`id` DESC
LIMIT 500

Currently with one transaction per user, it works fine. BTW with many transactions I still get the 1st entry from paypal_transactions table (the oldest, but I want the latest from now).

I did many tries, without success.

Thanks for your help !

Answer 1

Here you go:

SELECT `Transaction`.*, `User`.*, `Tipster`.`username`
FROM `pronostics_framework`.`users` AS `User`
LEFT JOIN `pronostics_framework`.`users` AS `Tipster` ON (`User`.`tipster_id` = `Tipster`.`id`)
LEFT JOIN (SELECT user_id, MAX(date_dt) AS max_date
            FROM `pronostics_framework`.paypal_transactions
            GROUP BY user_id) AS max_trans 
    ON User.id = max_trans.user_id
LEFT JOIN `pronostics_framework`.`paypal_transactions` AS `Transaction` 
    ON (max_trans.user_id = `Transaction`.`user_id` AND max_trans.max_date = Transation.date_dt)
ORDER BY `User`.`id` DESC
LIMIT 500

Another way, based on the first query in the first answer at Retrieving the last record in each group :

SELECT `Transaction`.*, `User`.*, `Tipster`.`username`
FROM `pronostics_framework`.`users` AS `User`
LEFT JOIN `pronostics_framework`.`users` AS `Tipster` ON (`User`.`tipster_id` = `Tipster`.`id`)
LEFT JOIN `pronostics_framework`.`paypal_transactions` AS `Transaction` ON Transaction.user_id = User.id
LEFT JOIN `pronostics_framework`.paypal_transactions AS Transactions1 
    ON Transactions1.user_id = Transactions.user_id AND Transactions1.user_id > Transactions.user_id
WHERE Transactions1.user_id IS NULL
ORDER BY `User`.`id` DESC
LIMIT 500