sql - 将 SQL 数据从单列返回到多列

Question

我有一个包含我感兴趣的两列的表格。

一列是日期，另一列是标记名。

我想将标记名返回到与相同日期匹配的不同列中。

我可以使用子查询来实现这一点，但是有没有更有效的方法来做到这一点？我说的是检索大约 20-30k 行，这会导致大约 300,000 个查询

选择插入以确保日期彼此对齐的最有效方法是什么。

这是我目前的疑问。 (我需要每个标记名的值在行中对齐)

谢谢

SELECT ah1.DateTime,ah1.Value as TPH,
(select value
from dbo.AnalogHistory
where tagname = 'LS_EM1_NXG.NXG_I'
and datetime = ah1.DateTime
) as EM1_Current,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM2_NXG.NXG_I'
and datetime = ah1.DateTime
) as EM2_Current,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM1_NXG.NXG_SPEED'
and datetime = ah1.DateTime
) as EM1_Speed,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM2_NXG.NXG_SPEED'
and datetime = ah1.DateTime
) as EM2_Speed,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM1_NXG.NXG_P'
and datetime = ah1.DateTime
) as EM1_Power,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM2_NXG.NXG_P'
and datetime = ah1.DateTime
) as EM2_Power,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM1_NXG.NXG_TRQ'
and datetime = ah1.DateTime
) as EM1_Torque,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM2_NXG.NXG_TRQ'
and datetime = ah1.DateTime
) as EM2_Torque,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM1_NXG.NXG_TRQ_UTIL'
and datetime = ah1.DateTime
) as EM1_Torque_U,

(select value
from dbo.AnalogHistory
where tagname = 'LS_EM2_NXG.NXG_TRQ_UTIL'
and datetime = ah1.DateTime
) as EM2_Torque_U,

(select value
from dbo.AnalogHistory
where tagname = 'LS_TE754001G.PVAI'
and datetime = ah1.DateTime
) as EM1_NDE,

(select value
from dbo.AnalogHistory
where tagname = 'LS_TE754001H.PVAI'
and datetime = ah1.DateTime
) as EM1_DE

  FROM [Runtime].[dbo].[AnalogHistory] ah1
  where TagName = 'CR_WQI752010.PVAI'
  and wwResolution = '600000'
  and DateTime > '20160816'
  and wwRetrievalMode = 'cyclic'

Answer 1

也许您可以使用条件聚合。像这样的事情:

select datetime,
       max(case when tagname = 'LS_EM1_NXG.NXG_I' then value end) as val1,
       . . .
from dbo.AnalogHistory
group by datetime ;