SQL Join users with transactions and rebills

SELECT u.first_name, u.last_name, u.user_name, u.phone, u.name, SUM(IF(t.status = "CONFIRMED", t.amount, 0) )AS sum,
       GROUP_CONCAT(CONCAT(t.payment_id, "-", t.amount, "-", t.status, "-", t.error_code, COALESCE(t.pan, 'null'), "-", COALESCE(t.exp_date, "null"), "-", t.time)) AS transactions,
       GROUP_CONCAT(CONCAT(r.rebill_id,  "-", r.amount, "-", r.active, "-", r.last_success_payment, "-", COALESCE(r.last_reject_payment, "null"), "-", r.error_count)) AS rebills
FROM users AS u
LEFT JOIN transactions t ON u.user_id = t.user_id
LEFT JOIN rebills      r ON u.user_id = r.user_id
GROUP BY first_name, last_name, user_name, phone, name