MySQL requires that you list the table being deleted from. And, you cannot re-use the table being deleted from. So, try this:
DELETE arn
FROM `acc_reg_num_db` arn JOIN
(SELECT account_id, key, MAX(value) as max_value
FROM acc_reg_num_db arn2
GROUP BY account_id, key
) arn2
USING (account_id, key)
WHERE arn.value < arn2.max_value AND
arn.key IN ('#betaminutes', '#online_minute');
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…