Question

我对SQL很新，所以请保持温和。我有一张桌子记录了各个地方各种传感器的温度。如果更容易，我很乐意重新安装数据库结构。

列为：ID int ，SensorID tinyint ，LocationID tinyint ，TempReadDT datetime ，Temp（< em>十进制4,1 ）

传感器每隔几分钟记录一次读数，我想有一个存储过程来获取以下信息，以便在摘要页面上显示：

当前室内温度（传感器1的最新读数）
当前室外温度（传感器2的最新读数）
过去24小时的平均室内温度
过去7天的室内平均温度
上次更新日期时间（记录的最新日期）

我已经创建了单独的SELECT语句（下面），但我不确定如何将它们组合成一个查询，以便在一行中返回数据。

SELECT TOP 1 Temp AS "intTemp"
  FROM Temperature
 WHERE SensorID = 1
 ORDER BY ID DESC

SELECT TOP 1 Temp AS "extTemp"
  FROM Temperature
 WHERE SensorID = 2
 ORDER BY ID DESC

SELECT AVG(Temp) AS "avgTemp24h"
  FROM Temperature
 WHERE SensorID = 1
   AND TempReadDT >= DATEADD(DAY,-1, SYSDATETIME())

SELECT AVG(Temp) AS "avgTemp7d"
  FROM Temperature
 WHERE SensorID = 1
   AND TempReadDT >= DATEADD(DAY,-7, SYSDATETIME())

SELECT MAX(TempReadDT)
  FROM Temperature

Answer 1

我讨厌交叉联接，但是......

Select * from 
(SELECT TOP 1 Temp AS "intTemp"
  FROM Temperature
 WHERE SensorID = 1
 ORDER BY ID DESC
) A
cross join
(SELECT TOP 1 Temp AS "extTemp"
  FROM Temperature
 WHERE SensorID = 2
 ORDER BY ID DESC
)B
cross join
(
SELECT AVG(Temp) AS "avgTemp24h"
  FROM Temperature
 WHERE SensorID = 1
   AND TempReadDT >= DATEADD(DAY,-1, SYSDATETIME())
)C
cross join
(
SELECT AVG(Temp) AS "avgTemp7d"
  FROM Temperature
 WHERE SensorID = 1
   AND TempReadDT >= DATEADD(DAY,-7, SYSDATETIME())
)D 
cross join
(
SELECT MAX(TempReadDT)
  FROM Temperature) E

应该有用。

Answer 2

SELECT 
   Max(case SensorID when 1 then Temp else null end) AS "intTemp",
   Max(case SensorID when 2 then Temp else null end) AS "intTemp",
   AVG(case 
           when SensorID = 1  
            AND TempReadDT >= DATEADD(DAY,-1, SYSDATETIME()) 
           then Temp else null end) AS "avgTemp24h",
   AVG(case 
           when SensorID = 1  
            AND TempReadDT >= DATEADD(DAY,-7, SYSDATETIME()) 
           then Temp else null end) AS "avgTemp7d",
   MAX(TempReadDT) MaxTemp
FROM Temperature

Answer 3

您可以使用子查询和别名结果，例如

SELECT t1.col1, t2.col2 from (select * from tbl1) as t1, (select * from tbl2) as t2

组合多个复杂的SELECT语句，使它们出现在一行上

3 个答案: