12345    credit           2016/01/01  amazon  450
23456    debit            2016/05/04  paypal  600

id       first_name      last_name        email
12345      Lisa            Green         lg@tr.com

First_Name    `Last_Name`   `First_Load`  `Second_Load`

SELECT
first_name,
last_name,
SUM(CASE WHEN posted_at = SELECT MIN(posted_at) FROM transaction AND t.transaction_type = 'Credit' AND t.memo LIKE '%amazon%' THEN BALANCE END) AS MINPOST
FROM user u LEFT OUTER JOIN transaction t
ON u.id = t.user_id
GROUP BY 1,2