Group data without changing query flow - sql

Question

For me it's hard to explait what do I want so article's name may be unclear, but I hope I can describe it with code.
I have some data with two most important value, so let it be time t and value f(t). It's stored in the table, for example
1 - 1000
2 - 1200
3 - 1100
4 - 1500
...
I want to plot a graph using it, and this graph should contain N points. If table has rows less than this N, then we just return this table. But if it hasn't, we should group this points, for example, N = Count/2, then for an example above:
1 - (1000+1200)/2 = 1100
2 - (1100+1500)/2 = 1300
...
I wrote an SQL script (it works fine for N >> Count) (MonitoringDateTime - is t, and ResultCount if f(t))
ALTER PROCEDURE [dbo].[usp_GetRequestStatisticsData]
#ResourceTypeID bigint,
#DateFrom datetime,
#DateTo datetime,
#EstimatedPointCount int
AS
BEGIN
SET NOCOUNT ON;
SET ARITHABORT ON;
declare #groupSize int;
declare #resourceCount int;
select #resourceCount = Count(*)
from ResourceType
where ID & #ResourceTypeID > 0
SELECT d.ResultCount
,MonitoringDateTime = d.GeneratedOnUtc
,ResourceType = a.ResourceTypeID,
ROW_NUMBER() OVER(ORDER BY d.GeneratedOnUtc asc) AS Row
into #t
FROM dbo.AgentData d
INNER JOIN dbo.Agent a ON a.CheckID = d.CheckID
WHERE d.EventType = 'Result' AND
a.ResourceTypeID & #ResourceTypeID > 0 AND
d.GeneratedOnUtc between #DateFrom AND #DateTo AND
d.Result = 1
select #groupSize = Count(*) / (#EstimatedPointCount * #resourceCount)
from #t
if #groupSize = 0 -- return all points
select ResourceType, MonitoringDateTime, ResultCount
from #t
else
select ResourceType, CAST(AVG(CAST(#t.MonitoringDateTime AS DECIMAL( 18, 6))) AS DATETIME) MonitoringDateTime, AVG(ResultCount) ResultCount
from #t
where [Row] % #groupSize = 0
group by ResourceType, [Row]
order by MonitoringDateTime
END
, but it's doesn't work for N ~= Count, and spend a lot of time for inserts.
This is why I wanted to use CTE's, but it doesn't work with if else statement.
So i calculated a formula for a group number (for use it in GroupBy clause), because we have
GroupNumber = Count < N ? Row : Row*NumberOfGroups
where Count - numer of rows in the table, and NumberOfGroups = Count/EstimatedPointCount
using some trivial mathematics we get a formula
GroupNumber = Row + (Row*Count/EstimatedPointCount - Row)*MAX(Count - Count/EstimatedPointCount,0)/(Count - Count/EstimatedPointCount)
but it doesn't work because of Count aggregate function:
Column 'dbo.AgentData.ResultCount' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
My english is very bad and I know it (and i'm trying to improve it), but hope dies last, so please advice.
results of query
SELECT d.ResultCount
, MonitoringDateTime = d.GeneratedOnUtc
, ResourceType = a.ResourceTypeID
FROM dbo.AgentData d
INNER JOIN dbo.Agent a ON a.CheckID = d.CheckID
WHERE d.GeneratedOnUtc between '2015-01-28' AND '2015-01-30' AND
a.ResourceTypeID & 1376256 > 0 AND
d.EventType = 'Result' AND
d.Result = 1
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Answer 1

Here's an example using NTILE and your simple sample data at the top of your question:
declare #samples table (ID int, sample int)
insert into #samples (ID,sample) values
(1,1000),
(2,1200),
(3,1100),
(4,1500)
declare #results int
set #results = 2
;With grouped as (
select *,NTILE(#results) OVER (order by ID) as nt
from #samples
)
select nt,AVG(sample) from grouped
group by nt
Which produces:
nt
-------------------- -----------
1 1100
2 1300
If #results is changed to 4 (or any higher number) then you just get back your original result set.
Unfortunately, I don't have your full data nor can I fully understand what you're trying to do with the full stored procedure, so the above would probably need to be adapted somewhat.

Answer 2

I haven't tried it, but how about instead of
select ResourceType, CAST(AVG(CAST(#t.MonitoringDateTime AS DECIMAL( 18, 6))) AS DATETIME) MonitoringDateTime, AVG(ResultCount) ResultCount
from #t
where [Row] % #groupSize = 0
group by ResourceType, [Row]
order by MonitoringDateTime
perhaps something like
select ResourceType, CAST(AVG(CAST(#t.MonitoringDateTime AS DECIMAL( 18, 6))) AS DATETIME) MonitoringDateTime, AVG(ResultCount) ResultCount
from #t
group by ResourceType, convert(int,[Row]/#groupSize)
order by MonitoringDateTime
Maybe that points you in some new direction? by converting to int we are truncating everything after the decimal so Im hoping that will give you a better grouping? you might need to put your row-number over resource type for this to work?