Question

我有以下查询构建记录集，该记录集在饼图中用作报告。

它不经常运行，但是当它运行时需要几秒钟，我想知道是否有任何方法可以提高效率。

SELECT
  CASE
    WHEN (lastStatus IS NULL)     THEN 'Unused'
    WHEN (attempts > 3 AND callbackAfter IS NULL)   THEN 'Max Attempts Reached'
    WHEN (callbackAfter IS NOT NULL AND callbackAfter >  DATE_ADD(NOW(), INTERVAL 7 DAY)) THEN 'Call Back After 7 Days'
    WHEN (callbackAfter IS NOT NULL AND callbackAfter <= DATE_ADD(NOW(), INTERVAL 7 DAY)) THEN 'Call Back Within 7 Days'
    WHEN (archived = 0)     THEN 'Call Back Within 7 Days'
    ELSE 'Spoke To'
  END AS statusSummary,
  COUNT(leadId) AS total
FROM
  CO_Lead
WHERE
  groupId = 123
  AND
  deleted = 0
GROUP BY
  statusSummary
ORDER BY
  total DESC;

我有（groupId, deleted）的索引，但我不确定将任何其他字段添加到索引中会有所帮助（如果可以的话，我该如何决定哪个字段应该先行？{ {1}}因为它使用最多？）

该表有大约500,000行（但从现在起每年将有10次。）

我能想到的唯一另一件事就是将它分成6个查询（WHEN子句移入WHERE），但这需要花费3倍的时间。

编辑：

这是表格定义

callbackAfter

Answer 1

尝试删除索引以查看是否可以提高性能。

在某些数据库中，索引不一定能提高性能。如果您有索引，MySQL将始终使用它。在这种情况下，这意味着它将读取索引，然后它将必须从每个页面读取数据。页面读取是随机的，而不是顺序的。对于必须读取所有页面的查询，此随机读取可以降低性能。

Answer 2

注意：

如果leadId不能NULL，请将COUNT(leadId)更改为COUNT(*)。它们在逻辑上是等价的，但大多数版本的MySQL优化器并不那么聪明，无法识别它。
删除两个冗余的callbackAfter IS NOT NULL条件。如果callbackAfter满足第二部分，则无论如何都不能为空。
您可以将查询拆分为6个部分并为每个部分添加适当的索引 - 但是，根据CASE的条件是否重叠，您可能会得到错误或正确的结果。

可能的重写（注意不同的格式并检查是否返回相同的结果，它可能不会！）

SELECT
    cnt1 AS "Unused"
  , cnt2 AS "Max Attempts Reached"
  , cnt3 AS "Call Back After 7 Days"
  , cnt4 AS "Call Back Within 7 Days"
  , cnt5 AS "Call Back Within 7 Days"
  , cnt6 - (cnt1+cnt2+cnt3+cnt4+cnt5) AS "Spoke To"
FROM
  ( SELECT
      ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
          AND lastStatus IS NULL
      ) AS cnt1
    , ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
          AND attempts > 3 AND callbackAfter IS NULL
      ) AS cnt2
    , ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
          AND callbackAfter >  DATE_ADD(NOW(), INTERVAL 7 DAY)
      ) AS cnt3
    , ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
          AND callbackAfter <= DATE_ADD(NOW(), INTERVAL 7 DAY)
      ) AS cnt4
    , ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
          AND archived = 0
      ) AS cnt5
    , ( SELECT COUNT(*)  FROM CO_Lead
        WHERE groupId = 123 AND deleted = 0
      ) AS cnt6
  ) AS tmp ;

如果它确实返回了正确的结果，您可以添加要用于每个子查询的索引：

对于子查询1：(groupId, deleted, lastStatus)

对于子查询2,3,4：(groupId, deleted, callbackAfter, attempts)

对于子查询5：(groupId, deleted, archived)

另一种方法是保留您的查询（仅注意上面的注释1和2）并添加一个宽覆盖索引：

 (groupId, deleted, lastStatus, callbackAfter, attempts, archived)

使用Case进行查询的效率更高的group by

2 个答案: