即使该时间没有条目，仍然显示正确的时间集答案

【问题标题】：Still show the proper set of time even if there's no entry for that time即使该时间没有条目，仍然显示正确的时间集
【发布时间】：2014-05-08 17:13:49
【问题描述】：

我有这个查询，它从上午 12 点到晚上 11:45 获取平均值并将值按 15 分钟分组。

SELECT FROM_UNIXTIME(t_stamp/1000, '%m/%d/%Y %l:%i %p') as t_stamp,
    ROUND(AVG(CASE WHEN id = '001' THEN value END),2) Value1,   
    ROUND(AVG(CASE WHEN id = '002' THEN value END),2) Value2,
    ROUND(AVG(CASE WHEN id = '003' THEN value END),2) Value3

FROM table1
WHERE tagid IN ("001", "002", "003") and

date(from_unixtime(t_stamp/1000)) BETWEEN "2014-05-01" AND "2014-05-01"

GROUP BY DATE(from_unixtime(t_stamp/1000)), HOUR(from_unixtime(t_stamp/1000)), MINUTE(from_unixtime(t_stamp/1000))  DIV 15

输出如下所示

    t_stamp             |   Value1  |   Value2  |   Value3
05/01/2014 12:00 AM     |   199     |   99      |   100
05/01/2014 12:15 AM     |   299     |   19      |   140
05/01/2014 12:30 AM     |   399     |   59      |   106
05/01/2014 12:45 AM     |   499     |   59      |   112
.
.
.
05/01/2014 11:00 PM     |   149     |   199     |   100
05/01/2014 11:15 PM     |   599     |   93      |   123
05/01/2014 11:30 PM     |   129     |   56      |   150
05/01/2014 11:45 PM     |   109     |   60      |   134

它工作正常，但我注意到有时如果像 12:30 这样的时间没有条目而不是显示

    t_stamp             |   Value1  |   Value2  |   Value3
05/01/2014 12:00 AM     |   199     |   99      |   100
05/01/2014 12:15 AM     |   299     |   19      |   140
05/01/2014 12:30 AM     |   Null    |   Null    |   Null
05/01/2014 12:45 AM     |   499     |   59      |   112

它会像这样显示一组时间：

    t_stamp             |   Value1  |   Value2  |   Value3
05/01/2014 12:00 AM     |   199     |   99      |   100
05/01/2014 12:15 AM     |   299     |   19      |   140
05/01/2014 12:33 AM     |   122     |   141     |   234
05/01/2014 12:45 AM     |   499     |   59      |   112

我希望发生的是，当 15 分钟组没有时间时，它仍会显示正确的时间集，然后仅在列值上显示 null。我想要的输出是这样的：

    t_stamp             |   Value1  |   Value2  |   Value3
05/01/2014 12:00 AM     |   199     |   99      |   100
05/01/2014 12:15 AM     |   299     |   19      |   140
05/01/2014 12:30 AM     |   Null    |   Null    |   Null
05/01/2014 12:45 AM     |   499     |   59      |   112

我该怎么做？

谢谢。

【问题讨论】：

标签： mysql time time-series missing-data

【解决方案1】：

您需要一个作为基数来源的表格作为开始。目前让我们假设它存在，它被称为cardinal。

然后，您需要创建一个查询（一个虚拟表），它将每十五分钟返回一次带有时间戳的行，从最早的相关时间戳开始，到最新的结束。以下是如何为您的查询执行此操作。

SELECT '2014-05-01' + INTERVAL (cardinal.n * 15) MINUTE as t_stamp
  FROM cardinal
 WHERE cardinal.n <= 24*4

然后你需要将该虚拟表加入到你现有的查询中，如下所示

SELECT DATE_FORMAT(t_stamp.t_stamp, '%m/%d/%Y %l:%i %p') t_stamp,
       ROUND(AVG(CASE WHEN id = '001' THEN value END),2) Value1,   
       ROUND(AVG(CASE WHEN id = '002' THEN value END),2) Value2,
       ROUND(AVG(CASE WHEN id = '003' THEN value END),2) Value3
  FROM table1 AS t
  LEFT JOIN (
        SELECT '2014-05-01' + INTERVAL (cardinal.n * 15) MINUTE as t_stamp
          FROM cardinal
         WHERE cardinal.n <= 24*4
       ) AS t_stamp 
         ON t_stamp.t_stamp = FROM_UNIXTIME(t.t_stamp/1000)   
 WHERE tagid IN ("001", "002", "003")
   AND date(from_unixtime(t_stamp/1000)) BETWEEN "2014-05-01" AND "2014-05-01"
 GROUP BY DATE(from_unixtime(t_stamp/1000)), 
          HOUR(from_unixtime(t_stamp/1000)), 
          MINUTE(from_unixtime(t_stamp/1000))  DIV 15

请注意，LEFT JOIN 可确保原始查询中的 NULL 值包含在结果集中。

现在，这个神奇的cardinal 表从何而来？

您可以将其生成为两个视图，如下所示。这个特殊的视图生成从 0 到 100 000 的数字，这对于一年的四分之一小时来说已经绰绰有余了。

CREATE OR REPLACE VIEW cardinal10 AS
    SELECT 0 AS N UNION
    SELECT 1 AS N UNION
    SELECT 2 AS N UNION
    SELECT 3 AS N UNION
    SELECT 4 AS N UNION
    SELECT 5 AS N UNION
    SELECT 6 AS N UNION
    SELECT 7 AS N UNION
    SELECT 8 AS N UNION
    SELECT 9 AS N;


CREATE OR REPLACE VIEW cardinal AS
    SELECT A.N + 10*(B.N + 10*(C.N + 10*(D.N + 10*(E.N)))) AS N
    FROM cardinal10 A,cardinal10 B,cardinal10 C, 
         cardinal10 D,cardinal10 E;

这是有关该主题的文章。 http://www.plumislandmedia.net/mysql/filling-missing-data-sequences-cardinal-integers/

【讨论】：