MySQL查詢查看性能下降

Question

我在視圖中使用了以下查詢：

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`

此查詢需要大約 4 秒才能加載，有關標簽的信息：

lora_message : 25k 行約 20 列

lora_device ：520 行約 10 列

通常我會說這對 mysql 來說不是問題，但由於某種原因，它運行得很慢。

Answer 1

嘗試添加索引

 create index ix_loramessage_rssi on lora_message(eui, rssi)
 create index ix_loramessage_db_timestamp on lora_message(eui, db_timestamp)

並使用

 count(`b`.`rssi`) AS `total_messages`,

代替

 count(`b`.`msg_id`) AS `total_messages`,

因為它應該在您的查詢中返回相同的結果