test.sql

# Move stats from new user to old user
UPDATE
    tb_user OldUser,
    (
     SELECT
        level,
        points,
        minutes_in_chat_online,
        minutes_in_chat_offline
    FROM tb_user
    WHERE
        username='mikkael') NewUser
SET
    OldUser.level=NewUser.level,
    OldUser.points+=NewUser.points,
    OldUser.minutes_in_chat_online+=NewUser.minutes_in_chat_online,
    OldUser.minutes_in_chat_offline+=NewUser.minutes_in_chat_offline
WHERE
    OldUser.username='mike_1311'
LIMIT 1;

# Remove new user
DELETE FROM tb_user WHERE username='mikkael' LIMIT 1;

# Update username of old user
UPDATE tb_user SET username='mikkael' WHERE username='mike_1311' LIMIT 1;

UPDATE
tb_user
SET
tb_user.level = NewUser.level,
tb_user.points = (tb_user.points + NewUser.points),
tb_user.minutes_in_chat_online = (tb_user.minutes_in_chat_online + NewUser.minutes_in_chat_online),
tb_user.minutes_in_chat_offline = (tb_user.minutes_in_chat_offline + NewUser.minutes_in_chat_offline)
INNER JOIN
(
SELECT
level,
points,
minutes_in_chat_online,
minutes_in_chat_offline
FROM tb_user
WHERE
username='mikkael'
LIMIT 1
) NewUser
WHERE
username='mike_1311'
LIMIT 1;