Group by day from a certain hour of the day - sql

Question

SQLServer 2008r2. I have a table which is populated with a record at 10 mins past every hour of every day. Every hour the job is run it also enters 48 records which represent a forecast of what is likely to happen for the next 48 hours. Note - Just before it enters the 48 hour forecast it deletes the forecast which was entered last time. So although it enters a 48 hour forecast every hour there is only ever one forecast in the system. The relevant fields in the table look like this:
currentScore obsDate
9 2017-06-22 08:10:00
9 2017-06-22 07:10:00
9 2017-06-22 06:10:00
10 2017-06-22 05:10:00
... ...
How can I query this table and group by day from a certain time of day? I would like the day to start at 6am the day before and finish at 6am on the day. I only need five records from the table, the day, two before and two in the future. So if its Jun 20 I want June 18, 19, 20, 21 and 22. Here is the query which gets the correct results by calendar day.
SELECT cast(obsDate AS DATE) AS theDate
,sum(CASE
WHEN currentScore < 8
THEN 1
ELSE 0
END) AS currentscore_low
,sum(CASE
WHEN currentScore >= 8
AND currentScore < 17
THEN 1
ELSE 0
END) AS currentscore_medium
,sum(CASE
WHEN currentScore >= 17
THEN 1
ELSE 0
END) AS currentscore_high
FROM diseaseScores
WHERE siteID = 8315
AND obsDate >= cast(getdate() - 2 AS DATE)
GROUP BY cast(obsDate AS DATE)
ORDER BY cast(obsDate AS DATE);
which returns this result:
theDAte low med high
2017-06-18 23 0 0
2017-06-19 22 0 0
2017-06-20 5 19 0
2017-06-21 0 24 0
2017-06-22 0 9 0
There is a new requirement to get the same result but the group by and the subsequent counts need to be from 6am to 6am. e.g
the first rec should be from 2017-06-17 06:00am to 2017-06-18 06:00am
the second rec should be from 2017-06-18 06:00am to 2017-06-19 06:00am
....etc
How can I do this? Thanks in advance
UPDATE, I have done two things:
1..introduce Tims idea
2..I also add an extra field 'numOfScores' to show how many hours worth of data
each line represent
select
cast(dateadd(hour, -6, obsDate) as date) as theDate, count(currentScore) as numOfScores,
sum(case when currentScore < 8 then 1 else 0 end) as currentscore_low,
sum(case when currentScore >= 8 and currentScore < 17
then 1 else 0 end) as currentscore_medium,
sum(case when currentScore >= 17 then 1 else 0 end) as currentscore_high
from diseaseScores
where siteID = 8315 and
obsDate >= cast(getdate() - 2 as date)
group by cast(dateadd(hour, -6, obsDate) as date)
order by cast(dateadd(hour, -6, obsDate) as date);
I now get this result:
2017-06-18 5 5 0 0
2017-06-19 24 23 1 0
2017-06-20 24 1 23 0
2017-06-21 24 8 16 0
2017-06-22 24 1 23 0
2017-06-23 9 0 9 0
This tells me that that there is only 5 hours worth of scores on the 2017-06-18. I want this first line to be 24 hours worth. From 6am on the 17th until 6am on the 18th. This makes me think I am not getting the result I wish
The 23rd only having 9 hours is ok because this is the most recent forecast
UPDATED:
I dont think its easily done in one query (if even possible) so I will just use five queries and specifically state the dates&times to get my outcome. e.g here are the first two:
select
sum(case when currentScore < 9 then 1 else 0 end) as numOfLOWRecs,
sum(case when currentScore > 8 and currentScore < 17 then 1 else 0 end) as currentscore_medium,
sum(case when currentScore >= 17 then 1 else 0 end) as currentscore_high
from diseaseScores where siteID = 9999
and obsDate >= '2017-06-18 06:00' and obsDate < '2017-06-19 06:00'
select
sum(case when currentScore < 9 then 1 else 0 end) as numOfLOWRecs,
sum(case when currentScore > 8 and currentScore < 17 then 1 else 0 end) as currentscore_medium,
sum(case when currentScore >= 17 then 1 else 0 end) as currentscore_high
from diseaseScores where siteID = 9999
and obsDate >= '2017-06-19 06:00' and obsDate < '2017-06-20 06:00'

Answer 1

One trick which might work here would be to simply shift each observation backwards by 6 hours. This would shift 2017-06-17 06:00:00 to 2017-06-17 00:00:00, i.e. now 6am becomes the start of that actual day.
select
cast(dateadd(hour, -6, obsDate) as date) as theDate,
sum(case when currentScore < 8 then 1 else 0 end) as currentscore_low,
sum(case when currentScore >= 8 and currentScore < 17
then 1 else 0 end) as currentscore_medium,
sum(case when currentScore >= 17 then 1 else 0 end) as currentscore_high
from diseaseScores
where siteID = 8315 and
obsDate >= cast(getdate() - 2 as date)
group by cast(dateadd(hour, -6, obsDate) as date)
order by cast(dateadd(hour, -6, obsDate) as date);