Splitting up group by with relevant aggregates beyond the basic ones? - sql

Question

I'm not sure if this has been asked before because I'm having trouble even asking it myself. I think the best way to explain my dilemma is to use an example.
Say I've rated my happiness on a scale of 1-10 every day for 10 years and I have the results in a big table where I have a single date correspond to a single integer value of my happiness rating. I say, though, that I only care about my happiness over 60 day periods on average (this may seem weird but this is a simplified example). So I wrap up this information to a table where I now have a start date field, an end date field, and an average rating field where the start days are every day from the first day to the last over all 10 years, but the end dates are exactly 60 days later. To be clear, these 60 day periods are overlapping (one would share 59 days with the next one, 58 with the next, and so on).
Next I pick a threshold rating, say 5, where I want to categorize everything below it into a "bad" category and everything above into a "good" category. I could easily add another field and use a case structure to give every 60-day range a "good" or "bad" flag.
Then to sum it up, I want to display the total periods of "good" and "bad" from maximum beginning to maximum end date. This is where I'm stuck. I could group by the good/bad category and then just take min(start date) and max(end date), but then if, say, the ranges go from good to bad to good then to bad again, output would show overlapping ranges of good and bad. In the aforementioned situation, I would want to show four different ranges.
I realize this may seem clearer to me that it would to someone else so if you need clarification just ask.
Thank you
---EDIT---
Here's an example of what the before would look like:
StartDate| EndDate| MoodRating
------------+------------+------------
1/1/1991 |3/1/1991 | 7
1/2/1991 |3/2/1991 | 7
1/3/1991 |3/3/1991 | 4
1/4/1991 |3/4/1991 | 4
1/5/1991 |3/5/1991 | 7
1/6/1991 |3/6/1991 | 7
1/7/1991 |3/7/1991 | 4
1/8/1991 |3/8/1991 | 4
1/9/1991 |3/9/1991 | 4
And the after:
MinStart| MaxEnd | Good/Bad
-----------+------------+----------
1/1/1991|3/2/1991 |good
1/3/1991|3/4/1991 |bad
1/5/1991|3/6/1991 |good
1/7/1991|3/9/1991 |bad
Currently my query with the group by rating would show:
MinStart| MaxEnd | Good/Bad
-----------+------------+----------
1/1/1991|3/6/1991 |good
1/3/1991|3/9/1991 |bad
This is something along the lines of
select min(StartDate), max(EndDate), Good_Bad
from sourcetable
group by Good_Bad

Answer 1

While Jason A Long's answer may be correct - I can't read it or figure it out, so I figured I would post my own answer. Assuming that this isn't a process that you're going to be constantly running, the CURSOR's performance hit shouldn't matter. But (at least to me) this solution is very readable and can be easily modified.
In a nutshell - we insert the first record from your source table into our results table. Next, we grab the next record and see if the mood score is the same as the previous record. If it is, we simply update the previous record's end date with the current record's end date (extending the range). If not, we insert a new record. Rinse, repeat. Simple.
Here is your setup and some sample data:
DECLARE #MoodRanges TABLE (StartDate DATE, EndDate DATE, MoodRating int)
INSERT INTO #MoodRanges
VALUES
('1/1/1991','3/1/1991', 7),
('1/2/1991','3/2/1991', 7),
('1/3/1991','3/3/1991', 4),
('1/4/1991','3/4/1991', 4),
('1/5/1991','3/5/1991', 7),
('1/6/1991','3/6/1991', 7),
('1/7/1991','3/7/1991', 4),
('1/8/1991','3/8/1991', 4),
('1/9/1991','3/9/1991', 4)
Next, we can create a table to store our results, as well as some variable placeholders for our cursor:
DECLARE #MoodResults TABLE(ID INT IDENTITY(1, 1), StartDate DATE, EndDate DATE, MoodScore varchar(50))
DECLARE #CurrentStartDate DATE, #CurrentEndDate DATE, #CurrentMoodScore INT,
#PreviousStartDate DATE, #PreviousEndDate DATE, #PreviousMoodScore INT
Now we put all of the sample data into our CURSOR:
DECLARE MoodCursor CURSOR FOR
SELECT StartDate, EndDate, MoodRating
FROM #MoodRanges
OPEN MoodCursor
FETCH NEXT FROM MoodCursor INTO #CurrentStartDate, #CurrentEndDate, #CurrentMoodScore
WHILE ##FETCH_STATUS = 0
BEGIN
IF #PreviousStartDate IS NOT NULL
BEGIN
IF (#PreviousMoodScore >= 5 AND #CurrentMoodScore >= 5)
OR (#PreviousMoodScore < 5 AND #CurrentMoodScore < 5)
BEGIN
UPDATE #MoodResults
SET EndDate = #CurrentEndDate
WHERE ID = (SELECT MAX(ID) FROM #MoodResults)
END
ELSE
BEGIN
INSERT INTO
#MoodResults
VALUES
(#CurrentStartDate, #CurrentEndDate, CASE WHEN #CurrentMoodScore >= 5 THEN 'GOOD' ELSE 'BAD' END)
END
END
ELSE
BEGIN
INSERT INTO
#MoodResults
VALUES
(#CurrentStartDate, #CurrentEndDate, CASE WHEN #CurrentMoodScore >= 5 THEN 'GOOD' ELSE 'BAD' END)
END
SET #PreviousStartDate = #CurrentStartDate
SET #PreviousEndDate = #CurrentEndDate
SET #PreviousMoodScore = #CurrentMoodScore
FETCH NEXT FROM MoodCursor INTO #CurrentStartDate, #CurrentEndDate, #CurrentMoodScore
END
CLOSE MoodCursor
DEALLOCATE MoodCursor
And here are the results:
SELECT * FROM #MoodResults
ID StartDate EndDate MoodScore
----------- ---------- ---------- --------------------------------------------------
1 1991-01-01 1991-03-02 GOOD
2 1991-01-03 1991-03-04 BAD
3 1991-01-05 1991-03-06 GOOD
4 1991-01-07 1991-03-09 BAD

Answer 2

Is this what you're looking for?
IF OBJECT_ID('tempdb..#MyDailyMood', 'U') IS NOT NULL
DROP TABLE #MyDailyMood;
CREATE TABLE #MyDailyMood (
TheDate DATE NOT NULL,
MoodLevel INT NOT NULL
);
WITH
cte_n1 (n) AS (SELECT 1 FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n (n)),
cte_n2 (n) AS (SELECT 1 FROM cte_n1 a CROSS JOIN cte_n1 b),
cte_n3 (n) AS (SELECT 1 FROM cte_n2 a CROSS JOIN cte_n2 b),
cte_Calendar (dt) AS (
SELECT TOP (DATEDIFF(dd, '2007-01-01', '2017-01-01'))
DATEADD(dd, ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) - 1, '2007-01-01')
FROM
cte_n3 a CROSS JOIN cte_n3 b
)
INSERT #MyDailyMood (TheDate, MoodLevel)
SELECT
c.dt,
ABS(CHECKSUM(NEWID()) % 10) + 1
FROM
cte_Calendar c;
--==========================================================
WITH
cte_AddRN AS (
SELECT
*,
RN = ISNULL(NULLIF(ROW_NUMBER() OVER (ORDER BY mdm.TheDate) % 60, 0), 60)
FROM
#MyDailyMood mdm
),
cte_AssignGroups AS (
SELECT
*,
DateGroup = DENSE_RANK() OVER (PARTITION BY arn.RN ORDER BY arn.TheDate)
FROM
cte_AddRN arn
)
SELECT
BegOfRange = MIN(ag.TheDate),
EndOfRange = MAX(ag.TheDate),
AverageMoodLevel = AVG(ag.MoodLevel),
CASE WHEN AVG(ag.MoodLevel) >= 5 THEN 'Good' ELSE 'Bad' END
FROM
cte_AssignGroups ag
GROUP BY
ag.DateGroup;
Post OP update solution...
WITH
cte_AddRN AS ( -- Add a row number to each row that resets to 1 ever 60 rows.
SELECT
*,
RN = ISNULL(NULLIF(ROW_NUMBER() OVER (ORDER BY mdm.TheDate) % 60, 0), 60)
FROM
#MyDailyMood mdm
),
cte_AssignGroups AS ( -- Use DENSE_RANK to create groups based on the RN added above.
-- How it works: RN set the row number 1 - 60 then repeats itself
-- but we dont want ever 60th row grouped together. We want blocks of 60 consecutive rows grouped together
-- DENSE_RANK accompolishes this by ranking within all the "1's", "2's"... and so on.
-- verify with the following query... SELECT * FROM cte_AssignGroups ag ORDER BY ag.TheDate
SELECT
*,
DateGroup = DENSE_RANK() OVER (PARTITION BY arn.RN ORDER BY arn.TheDate)
FROM
cte_AddRN arn
),
cte_AggRange AS ( -- This is just a straight forward aggregation/rollup. It produces the results similar to the sample data you posed in your edit.
SELECT
BegOfRange = MIN(ag.TheDate),
EndOfRange = MAX(ag.TheDate),
AverageMoodLevel = AVG(ag.MoodLevel),
GorB = CASE WHEN AVG(ag.MoodLevel) >= 5 THEN 'Good' ELSE 'Bad' END,
ag.DateGroup
FROM
cte_AssignGroups ag
GROUP BY
ag.DateGroup
),
cte_CompactGroup AS ( -- This time we're using dense rank to group all of the consecutive "Good" and "Bad" values so that they can be further aggregated below.
SELECT
ar.BegOfRange, ar.EndOfRange, ar.AverageMoodLevel, ar.GorB, ar.DateGroup,
DenseGroup = ar.DateGroup - DENSE_RANK() OVER (PARTITION BY ar.GorB ORDER BY ar.BegOfRange)
FROM
cte_AggRange ar
)
-- The final aggregation step...
SELECT
BegOfRange = MIN(cg.BegOfRange),
EndOfRange = MAX(cg.EndOfRange),
cg.GorB
FROM
cte_CompactGroup cg
GROUP BY
cg.DenseGroup,
cg.GorB
ORDER BY
BegOfRange;