MySQL查询查看速度慢

我在视图中使用了以下查询:

select `a`.`device_id` AS `device_id`,
       `a`.`alias` AS `alias`,
       `a`.`freq` AS `freq`,
       `a`.`gateway` AS `gateway`,
       `a`.`device_lat` AS`device_lat`,
       `a`.`device_long` AS `device_long`,
       `a`.`device_disabled` AS `device_disabled`,
       count(`b`.`msg_id`) AS `total_messages`,
       avg(`b`.`rssi`) AS `avg_rssi`,
       max(`b`.`db_timestamp`) AS `last_active`,
       (now() <= (max(`b`.`db_timestamp`) + interval 3 hour)) AS `device_status`
from `demo`.`lora_device` `a` 
left join `demo`.`lora_message` `b` on `a`.`device_id` = `b`.`eui` 
group by `a`.`device_id`

加载此查询大约需要4秒钟,有关选项卡的信息:

lora_设备:520行约10列

通常我会说这对mysql来说不是问题,但出于某种原因,它进展得很慢。