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我正在尝试编写一个查询来创建一个数据“表”，如下所示：

SELECT cs.`category_id`, cs.`ProcessDate`, cs.`PercentChange`
  FROM `Category_Statistics` cs
 WHERE cs.`ProcessDate` >= '2011-05-10'
   AND cs.`ProcessDate` <= '2011-05-14'

这将返回如下内容：

CategoryId  |  ProcessDate  | PercentChange
-------------------------------------------
category_4  |  2011-05-10   |      10
category_4  |  2011-05-11   |      18
category_4  |  2011-05012   |      12
...
category_7  |  2011-05-10   |      21
category_7  |  2011-05-11   |      7
...
category_12 |  2011-05-10   |      7
category_12 |  2011-05-11   |      15

现在我希望结果是这样的（来自 MySQL 查询，而不是由应用程序操作）：

CategoryId    | 2011-05-10 | 2011-05-11 | 2011-05-12 | 2011-05-13 | 2011-05-14 |
--------------------------------------------------------------------------------
category_4    |     10     |     18     |     12     |      9     |      14    |
category_7    |     21     |      7     |     16     |      14    |      13    |
categeory_12  |      7     |     15     |     11     |      19    |       8    |
--------------------------------------------------------------------------------

我有查询来构建上述结果。这是我的查询。

SELECT `CategoryId`,
   MAX(IF(c.`ProcessedOn` = '2011-04-20', c.`PercentChange`, NULL)) AS '2011-04-20',
   MAX(IF(c.`ProcessedOn` = '2011-04-21', c.`PercentChange`, NULL)) AS '2011-04-21',
   MAX(IF(c.`ProcessedOn` = '2011-04-22', c.`PercentChange`, NULL)) AS '2011-04-22',
   MAX(IF(c.`ProcessedOn` = '2011-04-23', c.`PercentChange`, NULL)) AS '2011-04-23',
   MAX(IF(c.`ProcessedOn` = '2011-04-24', c.`PercentChange`, NULL)) AS '2011-04-24'
  FROM `Category_Gravity` c
 WHERE c.`ProcessedOn` >= '2011-04-20'
   AND c.`ProcessedOn` <= '2011-04-24'
 GROUP BY `CategoryId`

当我有 20 或 100 条记录时，此查询工作正常。但是如果记录数是十万甚至更多，它就会变慢。我必须等待 10 分钟才能查看查询结果。请提供任何建议以加快我的查询或给我更好的查询来构建我的结果。

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