mysql性能低下

几天前我的mysql非常慢，一些sql查询不再工作，我不知道这个问题是从哪里来的

OS:Centos

MySQL:5.7-InnoDB

MySQL-V：

mysql版本14.14发行版5.7.28，适用于Linux（x86_64），使用EditLine包装器

这是我的问题

SELECT 
  BTCountry.id,
  BTCountry.name,
  BTCountry.code,
  BTCountry.last_data_from,
  BTCountry.year_last_data_from AS current_year,
  (SELECT 
    SUM(cantidad) AS subCount 
  FROM
    `krakente_marketpins`.`bt_countries` AS `subBTCountry` 
    INNER JOIN `krakente_marketpins`.`bus_trucks` AS `subBusTruck` 
      ON (
        `subBusTruck`.`pais_mercado_id` = `subBTCountry`.`id`
      ) 
  WHERE `subBusTruck`.`pais_mercado_id` = `BTCountry`.`id` 
    AND `subBusTruck`.`year_data_from` = 
      `subBTCountry`.`year_last_data_from`

    AND `subBusTruck`.month_data_from <= `subBTCountry`.`month_last_data_from`) AS ytd,
  (SELECT 
    SUM(cantidad) AS subCount 
  FROM
    `krakente_marketpins`.`bt_countries` AS `subBTCountry` 
    INNER JOIN `krakente_marketpins`.`bus_trucks` AS `subBusTruck` 
      ON (
        `subBusTruck`.`pais_mercado_id` = `subBTCountry`.`id`
      ) 
  WHERE `subBusTruck`.`pais_mercado_id` = `BTCountry`.`id` 
    AND `subBusTruck`.`year_data_from` = `subBTCountry`.`year_last_data_from` - 1 
    AND `subBusTruck`.`month_data_from` <= `subBTCountry`.`month_last_data_from`) AS last_year 
FROM
  bt_countries AS BTCountry 
  INNER JOIN `krakente_marketpins`.`bus_trucks` AS `BusTruck` 
    ON (
      `BusTruck`.`pais_mercado_id` = `BTCountry`.`id`
    ) 
WHERE `pais_mercado_id` IN (
    '1',
    '2',
    '3',
    '4',
    '5',
    '6',
    '7',
    '8',
    '9',
    '10',
    '11',
    '12'
  ) 
  AND mercado_id = ('1') 
GROUP BY `BTCountry`.`id` 
ORDER BY `ytd` DESC 

我之前说过，查询在几天前就开始工作了，但突然间，这不再工作了

另一方面，我有多个wp站点，这些站点突然变得非常慢，我认为它也来自mysql，因为如果我进入一个没有sql的站点，该站点工作正常

我可以从哪里开始检查

编辑

它的解释问题

---

这几乎是伪代码，但是，我打赌您可以在只传递一次数据的同时进行聚合。因为已经对数据进行了分组，所以不需要在select中再进行两次子查询

SELECT 
  BTCountry.id,
  BTCountry.name,
  BTCountry.code,
  BTCountry.last_data_from,
  BTCountry.year_last_data_from AS current_year,
  ytd =         SUM(CASE WHEN BusTruck.year_data_from = bt_countries.year_last_data_from - 1 AND bus_trucks.month_data_from <= bt_countries.month_last_data_from THEN cantidad ELSE NULL END),
  last_year =   SUM(CASE WHEN BusTruck.year_data_from = bt_countries.year_last_data_from AND bus_trucks.month_data_from <= bt_countries.month_last_data_from THEN cantidad ELSE NULL END)
FROM
  bt_countries AS BTCountry 
  INNER JOIN krakente_marketpins.bus_trucks AS BusTruck ON BusTruck.pais_mercado_id =BTCountry.id
WHERE
    pais_mercado_id IN (
    '1',
    '2',
    '3',
    '4',
    '5',
    '6',
    '7',
    '8',
    '9',
    '10',
    '11',
    '12'
  ) 
  AND mercado_id = ('1') 
GROUP 
    BYBTCountry.id,
    BTCountry.name,
    BTCountry.code,
    BTCountry.last_data_from,
    BTCountry.year_last_data_from
ORDER 
    BYytd 
DESC 

选择
BTCountry.id，
BTCountry.name，
BTCountry.code，
BTCountry.last_数据来自，
BTCountry.year\u上一个\u数据\u来自当前\u年，
年初至今=总和（当BusTruck.year\u data\u from=bt\u countries.year\u last\u data\u from-1和bus\u trucks.month\u data\u from这是一个非常庞大的查询时，首先要在当前的SELECT查询中运行
EXPLAIN SELECT…
。查看是否可以识别任何明显的瓶颈。使用
EXPLAIN
查看查询执行计划。典型的性能方面的问题是MySQL没有使用合适的索引，但是SQL性能比提供合适的索引要深刻得多。我忘了，我用解释查询更新了这个问题，我在pic中添加了它，因为我不知道如何使它成为tabletry executing
analyze table krakente_marketpins.bt_countries，krakente_marketpins.bus_trucks
然后重新尝试您的查询。分析说可以，但查询仍然是无限加载的，我忘了在localhost中使用
10.1.38-MariaDB-源代码分发正确地提到此查询工作
谢谢！我仍然不明白我的查询是如何工作的，突然查询崩溃了！@hansz请发布一篇帖子）显示创建表格bt_国家；和B）显示创建表格bus_卡车；C）解释SELECT（Ross Bush查询），这样我们就可以通过减少用于结果的行来看到改进。谢谢
SELECT 
  BTCountry.id,
  BTCountry.name,
  BTCountry.code,
  BTCountry.last_data_from,
  BTCountry.year_last_data_from AS current_year,
  ytd =         SUM(CASE WHEN BusTruck.year_data_from = bt_countries.year_last_data_from - 1 AND bus_trucks.month_data_from <= bt_countries.month_last_data_from THEN cantidad ELSE NULL END),
  last_year =   SUM(CASE WHEN BusTruck.year_data_from = bt_countries.year_last_data_from AND bus_trucks.month_data_from <= bt_countries.month_last_data_from THEN cantidad ELSE NULL END)
FROM
  bt_countries AS BTCountry 
  INNER JOIN krakente_marketpins.bus_trucks AS BusTruck ON BusTruck.pais_mercado_id =BTCountry.id
WHERE
    pais_mercado_id IN (
    '1',
    '2',
    '3',
    '4',
    '5',
    '6',
    '7',
    '8',
    '9',
    '10',
    '11',
    '12'
  ) 
  AND mercado_id = ('1') 
GROUP 
    BYBTCountry.id,
    BTCountry.name,
    BTCountry.code,
    BTCountry.last_data_from,
    BTCountry.year_last_data_from
ORDER 
    BYytd 
DESC