我如何在mysql中优化这个查询？

Posted 2023-03-24

【中文标题】我如何在mysql中优化这个查询？

【英文标题】：How i can optimize this query in mysql?

【发布时间】：2014-06-30 12:46:34

【问题描述】：

我有一个这样的查询 -

    SELECT 
  CONCAT(u.name, u.deviceAlias),
  u.name,
  u.deviceAlias,
  j.description,
  u.description AS vlanDescription 
FROM
  vlaninterfaces u,
  interfacedescriptioninfo j 
WHERE u.interfacedescriptioninfoid = j.id
  AND u.deviceId = j.deviceId 
  AND u.interfaceNameAlias = j.name 
  AND j.toDevice NOT IN 
  (SELECT 
    deviceAlias 
  FROM
    devices 
  WHERE siteId = 12) 
  AND u.deviceAlias IN 
  (SELECT 
    deviceAlias 
  FROM
    devices 
  WHERE siteId = 12) 
  AND CONCAT(u.name, u.deviceAlias) NOT IN 
  (SELECT DISTINCT 
    CONCAT(v.name, fromDevice) 
  FROM
    vlaninterfaces v,
    interfacedescriptioninfo i 
  WHERE v.interfacedescriptioninfoid = i.id
    AND v.deviceId = i.deviceId 
    AND v.interfacenameAlias = i.name 
    AND v.deviceAlias IN 
    (SELECT 
      deviceAlias 
    FROM
      devices 
    WHERE siteId = 12) 
    AND v.interfacenameAlias LIKE '%ae%' 
    AND IF(
      i.toDevice IS NULL,
      i.interconnectedDevice,
      i.toDevice
    ) IN 
    (SELECT 
      deviceAlias 
    FROM
      devices 
    WHERE deviceClass = 'SWITCH' 
      AND siteId = 12)) 
GROUP BY CONCAT(u.name, u.deviceAlias) ;

我尝试使用 MINUS 但在 mysql 中发现我们不能使用这样的集合运算符。

在解释计划中，使用不使用键并扫描所有行的表 vlaninterfaces。

请通过示例告诉我 NOT IN 的替代方法（如果可能，请使用相同的查询）。

【参考方案1】：

您的查询很复杂，所以我只展示一部分。可以将 LEFT JOIN 加入表并检查 null 而不是使用 NOT IN。 IE。如果我们有查询：

 SELECT 
  CONCAT(u.name, u.deviceAlias),
  u.name,
  u.deviceAlias,
  j.description,
  u.description AS vlanDescription 
FROM
  vlaninterfaces u,
  interfacedescriptioninfo j 
WHERE u.interfacedescriptioninfoid = j.id
  AND u.deviceId = j.deviceId 
  AND u.interfaceNameAlias = j.name 
  AND j.toDevice NOT IN 
  (SELECT 
    deviceAlias 
  FROM
    devices 
  WHERE siteId = 12) 

然后我们可以使用 siteId 12 加入设备别名，并检查在 where 子句中加入是否成功（注意在下面的示例中，我还将 vlaninterfaces 和 interfacedescriptioninfo 上的加入更改为显式 - 我发现这更具可读性):

SELECT 
  CONCAT(u.name, u.deviceAlias),
  u.name,
  u.deviceAlias,
  j.description,
  u.description AS vlanDescription 
FROM
  vlaninterfaces u
  INNER JOIN interfacedescriptioninfo j ON (u.interfacedescriptioninfoid = j.id AND u.deviceId = j.deviceId AND u.interfaceNameAlias = j.name )
  LEFT JOIN devices da ON (j.toDevice = da.deviceAlias AND da.siteId = 12)
WHERE 
   da.deviceAlias IS NULL

【参考方案2】：

好的，这需要大量的试验和错误，但我总是尝试将 IN 子句重写为连接，从而避免隐式子查询。 NOT IN 也是如此，您可以用 LEFT JOIN + WHERE 替换为 NULL

SELECT 
  CONCAT(u.name, u.deviceAlias),
  u.name,
  u.deviceAlias,
  j.description,
  u.description AS vlanDescription 
FROM
  vlaninterfaces u 
  JOIN   interfacedescriptioninfo j ON u.interfacedescriptioninfoid = j.id AND u.deviceId = j.deviceId AND u.interfaceNameAlias = j.name 
  JOIN devices d2 ON d2.deviceAlias=u.deviceAlias AND d2.siteId=12
  LEFT JOIN devices d1 ON d1.deviceAlias=j.toDevice AND d1.siteId = 12
  LEFT JOIN  (SELECT DISTINCT v.name, fromDevice
              FROM
              vlaninterfaces v,
              JOIN  interfacedescriptioninfo i ON v.interfacedescriptioninfoid = i.id   AND v.deviceId = i.deviceId   AND v.interfacenameAlias = i.name 
              JOIN devices d3 ON d3.deviceAlias=v.deviceAlias AND d3.siteId=12
              JOIN devices d4 ON d4.deviceAlias=IF(i.toDevice IS NULL,  i.interconnectedDevice,  i.toDevice) AND d4.siteId=12 AND d4.deviceClass = 'SWITCH' 
              WHERE v.interfacenameAlias LIKE '%ae%' 
            ) as subquery ON u.name=subquery.name AND u.deviceAlias=subquery.fromDevice

WHERE d1.deviceAlias is NULL -- this replaces the first NOT IN
and subquery.name is NULL  -- this replaces the second NOT IN

通过两个字段的连接查询实际上是丢弃索引。你不需要这样做。

最后，通过 name 和 deviceAlias 的 concat 分组在这里没有意义，因为您在 select 中没有任何聚合函数。