Question

I have this DB table in which data is constantly being added to. The Data that is being added is sensor data so there are two readings per sensor per hour. I would like to know of a way to get only the last reading of the day for the entire month. For example,

select * from dbo.NewLogTable
where Sensor_ID= '12345'and Date_Reading between '2012-08-01' and '2012-08-31' 
and DateTimeStamp between '23:30:00'and '23:59:00'
order by DateTimeStamp asc

I know this doesn’t work but its a pseudo code of what I want. Again the goal here is to get just one reading(the latest) per day for a particular sensor. I have seen plenty of example where the first and last day of the month are displayed, display past x amount of days, etc. Not really like my application. Can anyone help? thanks.

Answer 1

WITH
  sequenced AS
(
  SELECT
    ROW_NUMBER() OVER (PARTITION BY sensor_id, Date_Reading ORDER BY DateTimeStamp DESC) AS daily_sequence_id,
    *
  FROM
    dbo.NewLogTable
)
SELECT
  *
FROM
  sequenced
WHERE
  sensor_id = '12345'
  AND Date_Reading BETWEEN '2012-08-01' AND '2012-08-31'
  AND daily_sequence_id = 1