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# Simple query

Hej,

MS SQL Server 2008.

I have a table that records patient visits.  This table has three columns:

visit_date - the date of the visit

clinic_id - the identity of the clinic where the visit was made

npi_points - a value we measure for the patient on each visit.

Can someone help me with a query that returns the average change in npi_points between the 1st and 2nd visits, 1st and 3rd visits, and 1st and 4th visit?

I also need the same values for a clinic that has an id of 0.

Something likes this:

``````Visit        Total average change          Clinic "0" average change
2nd          12.34                                   11,54
3rd          15.98                                    14,74
4th          18,65                                     18,6
``````
0
soozh
• 2
• 2
• 2
• +1
1 Solution

Commented:
Can you give some examples of data in the actual table? Also will you please define the average change between one visit and another, how you calculate that value?
0

Commented:
how do you relate the visits to the same patient?  (surely you've got a patient id on the table as well?)
how/which patient at clinic 0 are the results to be shown with?

what happens if there are more or less than 4 visits?

can the patient change clinic's between visits , and what do you want to happen in those cases?

some example data and the expected result would assist.

... is there any time period for a vist to have occurred within to either exclude from the process or that would reset the visit sequence...

e.g. do you expect the visits to occur normally on a monthly basis ... and would ignore/reset if visits  had a gap of 6 months say?
0

Commented:
taking a leap, I assume there is also a patient_id involved, and the the 1st, 2nd, 3rd, 4th visits have to be aligned by patient. with some random numbers and guesswork, does this help? Note the output here is one row per clinic.
``````    CREATE TABLE pat_visits
([id] int, [patient_id] int, [visit_date] datetime, [clinic_id] int, [npi_points] decimal(5,2))
;

INSERT INTO pat_visits
([id], [patient_id], [visit_date], [clinic_id], [npi_points])
VALUES
(1, 111001, '2013-02-01 00:00:00', 2001, 12.09),
(2, 111002, '2013-02-01 00:00:00', 2001, 15.75),
(3, 111001, '2013-03-03 00:00:00', 2001, 7.16),
(4, 111002, '2013-04-02 00:00:00', 2001, 17.52),
(5, 111001, '2013-05-02 00:00:00', 2001, 5.06),
(6, 111002, '2013-06-01 00:00:00', 2001, 9.11),
(7, 111001, '2013-07-01 00:00:00', 2001, 13.93),
(8, 111002, '2013-07-31 00:00:00', 2001, 13.73),
(9, 111001, '2013-08-30 00:00:00', 2001, 10.39),
(10, 111002, '2013-09-29 00:00:00', 2001, 9.06),
(11, 111001, '2013-10-29 00:00:00', 2001, 11.66),
(12, 111002, '2013-11-28 00:00:00', 2001, 16.35),
(13, 111001, '2013-12-28 00:00:00', 2001, 11.97),
(14, 111002, '2014-01-27 00:00:00', 2001, 12.69),
(15, 111001, '2014-02-26 00:00:00', 2001, 8.35),
(16, 111002, '2014-03-28 00:00:00', 2001, 11.86),
(17, 111001, '2014-04-27 00:00:00', 2001, 7.74),
(18, 111002, '2014-05-27 00:00:00', 2001, 6.18),
(19, 111001, '2014-06-26 00:00:00', 2001, 6.19),
(20, 111002, '2014-07-26 00:00:00', 2001, 16.84)
;

**Query 1**:

WITH
CTE AS (
SELECT
*
, row_number() over (partition BY patient_id ORDER BY visit_date ASC) AS rn
FROM pat_visits
)
SELECT
clinic_id
, avg(v2change) AS v2change
, avg(v3change) AS v3change
, avg(v4change) AS v4change
FROM (
SELECT
v1.patient_id
, v1.clinic_id
, v2.npi_points - v1.npi_points AS v2change
, v3.npi_points - v2.npi_points AS v3change
, v4.npi_points - v3.npi_points AS v4change
FROM CTE AS v1
INNER JOIN CTE AS v2 ON v1.patient_id = v2.patient_id AND v1.rn = 1 AND v2.rn = 2
INNER JOIN CTE AS v3 ON v1.patient_id = v3.patient_id AND v2.rn = 2 AND v3.rn = 3
INNER JOIN CTE AS v4 ON v1.patient_id = v4.patient_id AND v3.rn = 3 AND v4.rn = 4
) AS v
GROUP BY
clinic_id

**[Results][2]**:

| CLINIC_ID | V2CHANGE | V3CHANGE | V4CHANGE |
|-----------|----------|----------|----------|
|      2001 |    -1.58 |   -5.255 |    6.745 |

[1]: http://sqlfiddle.com/#!3/723f7/1
``````
0

Commented:
more like this perhaps?

but you do need to explain what is meant by a clinic
and what date ranges you will eventually be applying this to...

`````` ;WITH
CTE AS (
SELECT
x.*
, row_number() over (partition BY patient_id ,clinic_id
ORDER BY visit_date ASC) AS rn
FROM pat_visits as x
)
SELECT
v2.rn
, Avg(case when v1.clinic_id = 0 then null else v2.npi_points - v1.npi_points end) as AvgChange
, Avg(case when v1.clinic_id = 0 then v2.npi_points - v1.npi_points else null end) as clinic0
FROM CTE AS v1
INNER JOIN CTE AS v2
ON v1.patient_id = v2.patient_id
AND v1.rn = 1 AND v2.rn in (2,3,4)
group by v2.rn
order by v2.rn

``````
0

Commented:
I see I missed the differences being from the 1st visit in all cases.

but perhaps also that the row_number() should be partitioned by both clinic and patient, in case a client moves between clinics
``````WITH
CTE AS (
SELECT
*
, row_number() over (partition BY clinic_id, patient_id ORDER BY visit_date ASC) AS rn
FROM pat_visits
)
SELECT
clinic_id
, avg(v2change) AS v2change
, avg(v3change) AS v3change
, avg(v4change) AS v4change
FROM (
SELECT
v1.patient_id
, v1.clinic_id
, v2.npi_points - v1.npi_points AS v2change
, v3.npi_points - v1.npi_points AS v3change
, v4.npi_points - v1.npi_points AS v4change
FROM CTE AS v1
INNER JOIN CTE AS v2 ON v1.clinic_id = v2.clinic_id AND v1.patient_id = v2.patient_id AND v2.rn = 2
INNER JOIN CTE AS v3 ON v1.clinic_id = v3.clinic_id AND v1.patient_id = v3.patient_id AND v3.rn = 3
INNER JOIN CTE AS v4 ON v1.clinic_id = v4.clinic_id AND v1.patient_id = v4.patient_id AND v4.rn = 4
) AS v
GROUP BY
clinic_id
;

-- http://sqlfiddle.com/#!3/723f7/9
``````
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Author Commented:
sorry for the lack of feedback... i am on holiday in London... but i will look at the solutions later tonight.
0

Author Commented:
100% as usual.
0
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