选择查询以获取两列中的唯一单元格

Question

I have an SQL Server database, that logs weather device sensor data.

The table looks like this:

Id DeviceId SensorId Value 1 1 1 42 2 1 1 3 3 1 2 30 4 2 2 0 5 2 1 1 6 3 1 26 7 3 1 23 8 3 2 1

In return the query should return the following:

Id DeviceId SensorId Value 2 1 1 3 3 1 2 30 4 2 2 0 5 2 1 1 7 3 1 23 8 3 2 1

For each device the sensor should be unique. ie Values in Columns DeviceId and SensorId should be unique (row-wise).

Apologies if I'm not clear enough.

Answer 1

If you don't want to sum Value as your desired result suggest, so you just want to take an "arbitrary" row of each "DeviceId + SensorId"-group:

WITH CTE AS
(
    SELECT Id, DeviceId, SensorId, Value,
           RN = ROW_NUMBER() OVER (PARTITION BY DeviceId, SensorId ORDER BY ID DESC)
    FROM dbo.TableName
)
SELECT Id, DeviceId, SensorId, Value
FROM CTE
WHERE RN = 1
ORDER BY ID

This returns the row with the highest ID per group. You need to change ORDER BY ID DESC if you want a different result. Demo: http://sqlfiddle.com/#!6/8e31b/2/0 (your result)