为所有给定的 ID 选择一个月内的最后一个值 [英] Select last value in a month for all given IDs

问题描述

我有 2 个表，一个包含仪表 ID，另一个包含第一个表中某些仪表的测量值.这是表结构:

I have 2 tables, one containing meter IDs, and another containing measurements for some of the meters in the first table. This is the table structure:

仪表配置:

• MeterID (int)
• MeterNumber (char[16])
• 类型 (char[25])

阅读:

• MeterID (int)
• 日期(日期时间)
• 值(数字(18,6))

我需要获取每个仪表的给定时间段的最后读数(及其日期)以及仪表编号.我设法在 T-SQL 中做到了这一点，尽管我对使用此查询的方式并不特别满意:

I need to get the last reading (and its date) from a given period for each meter, as well as the meter number. I managed to do this in T-SQL, although I'm not particularly pleased with the way I did it using this query:

select distinct
 cfg.MeterNumber,
 (select top 1 r.Date from Readings as r where r.Date between @startdate and @endDate and r.MeterID = cfg.MeterID order by r.Date desc) as Date,
 (select top 1 r.Value from Readings as r where r.Date between @startdate and @endDate and r.MeterID = cfg.MeterID order by r.Date desc) as Value
from
 MeterConfig cfg, Readings r1
where cfg.MeterID = r1.MeterID and r1.Date between @startdate and @endDate;

我怎样才能更有效地做到这一点?

How can I do this more efficiently?

推荐答案

WITH CTE AS (
SELECT mc.MeterID, Date, Value, ROW_NUMBER() OVER (PARTITION BY mc.MeterID ORDER BY Date DESC) as Rank
FROM  MeterConfig mc
INNER JOIN Readings rd
ON mc.MeterID = rd.MeterID
WHERE rd.Date BETWEEN @startdate AND @endDate)
SELECT * FROM CTE WHERE Rank = 1

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