How can I select one row of data per hour? - sql

Question

I'm new at sql.
There is something that makes me confused, i got data per minute, but i only need a row of it per hour or per 2 hours. For example when i select data from the previous day, it shows me 1440 rows and i need to reduce them to less rows to make some charts.
Thanks in advance.
when i use this query:
select [Value],[Time] from [AbsoluteData] where [Sensor] = '5100' and [Time] >= dateadd(day,datediff(day,1,GETDATE()),0) AND[Time] < dateadd(day, datediff(day, 0, GETDATE()), 0)
i got:

Answer 1

You can select on row per hour by using row_number() like this:
select t.*
from (select t.*,
row_number() over (partition by cast(datetimecol as date), datepart(hour, datetimecol)
order by datetimecol
) as seqnum
from t
) t
where seqnum = 1;
I cannot read your image and you don't have a sample query or sample data, so this uses generic names.

Answer 2

If the data drops in every minute and you want just one within a given range (last hour or last day), just restrict the rows to the range and pick 1:
select top 1
[Value], [Time]
from [AbsoluteData]
where [Sensor] = '5100'
and cast(Time as date) = cast(dateadd(day, -1, getdate()) as date)
order by Time desc;
(last one yesterday)
or:
set rowcount 1;
select [Value], [Time]
from [AbsoluteData]
where [Sensor] = '5100'
and cast(Time as date) = cast(dateadd(day, -1, getdate()) as date)
order by Time desc;
set rowcount 0;