我正在尝试针对在grafana仪表板中使用的MySQL数据库编写查询。当我从表中手动选择一个已知的时间戳时,我有一个有效的查询,但是当我事先不知道该时间戳时,我的数据是不正确的。
目标是获得仅使用1个TimeStmp即可获得4个不同名称中的UsedSpaceMB总量。即在TimeStmp之类的“%2018-07-27 16%”中。如果查询中包含多个TimeStmp,则UsedpaceMB的总量不正确。
表名称为存储
字段是TimeStmp,UsedSpaceMB和Name
Select TimeStmp, UsedSpaceMB, Name FROM Storage LIMIT 5;
+---------------------+-------------+------------------------+
| TimeStmp | UsedSpaceMB | Name |
+---------------------+-------------+------------------------+
| 2018-07-27 16:02:07 | 61415607 | Array1 |
| 2018-07-27 20:02:09 | 61896587 | Array1 |
| 2018-07-28 00:02:17 | 61767053 | Array1 |
| 2018-07-28 04:02:04 | 62175704 | Array1 |
| 2018-07-28 08:02:10 | 62683011 | Array1 |
+---------------------+-------------+------------------------+
SELECT DISTINCT NAME FROM Storage ORDER BY Name ASC;
+------------------------------+
| NAME |
+------------------------------+
| Array1 |
| Array2 |
| Array3 |
| Array4 |
+------------------------------+
该查询有效:
SELECT
TimeStmp as time,
'Used Capacity' as metric,
(SELECT SUM(UsedSpaceMB) as value)
FROM Storage
WHERE TimeStmp LIKE "%2018-07-27 16:%" AND Name IN ("Array1", "Array2", "Array3", "Array4")
(示例将To Time设置为2018-08-15 04:00的示例)
SELECT
TimeStmp as time,
'Used Capacity' as metric,
(SELECT SUM(UsedSpaceMB) as value)
FROM Storage
WHERE TimeStmp >= FROM_UNIXTIME($__unixEpochTo(),'%Y-%m-%d %H') AND Name IN ("Array1", "Array2", "Array3", "Array4")
我真正想做的是首先在原始查询中选择MAX(TimeStmp),然后在WHERE子句中使用它,以便我仅搜索1个特定的TimeStmp(即WHERE TimeStmp = MAX(TimeStmp)或HAVING TimeStmp = MAX(TimeStmp)。我不确定如何执行JOIN或使用HAVING,因为执行此查询时没有任何结果。
SELECT
TimeStmp as time,
'Used Capacity' as metric,
(SELECT SUM(UsedSpaceMB) as value)
FROM Storage
WHERE Name IN ("Array1", "Array2", "Array3", "Array4")
HAVING TimeStmp = MAX(TimeStmp)
预期结果:
SELECT (SELECT SUM(UsedSpaceMB)) FROM Storage WHERE TimeStmp LIKE "%2018-07-27 16:%" AND Name IN('Array1','Array2','Array3','Array4');
+---------------------------+
| (SELECT SUM(UsedSpaceMB)) |
+---------------------------+
| 777379124 |
+---------------------------+
最佳答案
如果要按名称对UsedSpaceMB行的总和(假定每个名称有多个行,则为一个时间戳):
SELECT
a.`Name`,
a.`TimeStamp` as `time`,
'Used Capacity' as `metric`,
SUM(a.`UsedSpaceMB`) as `value`
FROM `Storage` a
JOIN (SELECT MAX(`TimeStamp`) as `tm`,`Name`
FROM `Storage`
WHERE `Name` IN ("Array1", "Array2", "Array3", "Array4")
) b
ON a.`TimeStamp` = b.`tm` AND a.`Name` = b.`Name`
GROUP BY a.`Name`
ORDER BY a.`Name`
另外,不确定何时可以使用
(SELECT SUM(UsedSpaceMB) as value)
时为什么使用SUM(UsedSpaceMB) as value
。