How to Calculate Median? - sql-server

Question

I need to calculate a median on a set of data, so I created a temp table and have tried to follow some articles online with zero success, here is what I am working with:
CREATE TABLE #QuizTemp (QuizProfileID INT,Cnt INT,TotalScore INT)
INSERT INTO #QuizTemp
SELECT QuizAnswers.QuizProfileID, COUNT(QuizAnswers.QuizProfileID) AS Cnt, SUM(QuizAnswers.AnsweredYes) As TotalScore
FROM QuizAnswers INNER JOIN
Quizzes ON QuizAnswers.QuizID = Quizzes.QuizID
WHERE (Quizzes.PartnerID = 16)
GROUP BY QuizAnswers.QuizProfileID
HAVING COUNT(QuizAnswers.QuizProfileID)= 5
SELECT COUNT(*) AS CNT, Avg(TotalScore) AS AvgTotalScore FROM #QuizTemp
DROP TABLE #QuizTemp
The average works great and now I need the Median.

Answer 1

try capturing the row count on INSERT and then select the row that is in the middle using ROW_NUMBER():
CREATE TABLE #QuizTemp (QuizProfileID INT,Cnt INT,TotalScore INT)
DECLARE #Rows int
INSERT INTO #QuizTemp
SELECT QuizAnswers.QuizProfileID, COUNT(QuizAnswers.QuizProfileID) AS Cnt, SUM(QuizAnswers.AnsweredYes) As TotalScore
FROM QuizAnswers INNER JOIN
Quizzes ON QuizAnswers.QuizID = Quizzes.QuizID
WHERE (Quizzes.PartnerID = 16)
GROUP BY QuizAnswers.QuizProfileID
HAVING COUNT(QuizAnswers.QuizProfileID)= 5
DECLARE #Rows int
SELECT #Rows=##Rowcount
;with allrows as
(
SELECT TotalScore, ROW_NUMBER() (ORDER BY TotalScore) AS RowNumber
)
SELECT #Rows AS CNT, TotalScore AS MedianScore
FROM allrows WHERE RowNumber=#Rows/2
DROP TABLE #QuizTemp
EDIT
Here is a solution without a temp table:
DECLARE #YourTable table (TotalScore int)
INSERT INTO #YourTable Values (1)
INSERT INTO #YourTable Values (2)
INSERT INTO #YourTable Values (3)
INSERT INTO #YourTable Values (40)
INSERT INTO #YourTable Values (50)
INSERT INTO #YourTable Values (60)
INSERT INTO #YourTable Values (70)
;with allrows as
(
SELECT
TotalScore, ROW_NUMBER() OVER (ORDER BY TotalScore) AS RowNumber
FROM #YourTable
)
,MaxRows AS
(SELECT MAX(RowNumber) AS CNT,CONVERT(int,ROUND(MAX(RowNumber)/2.0,0)) AS Middle FROM allrows)
SELECT
m.CNT
,(SELECT AVG(TotalScore) FROM allrows) AS AvgTotalScore
,a.TotalScore AS Median
,m.Middle AS MedianRowNumber
FROM allrows a
CROSS JOIN MaxRows m
WHERE a.RowNumber=m.Middle
OUTPUT:
CNT AvgTotalScore Median MedianRowNumber
-------------------- -------------------- ----------- --------------------
7 32 40 4
(1 row(s) affected)
if you edit the first CTE to be:
;with allrows as
(
SELECT QuizAnswers.QuizProfileID, COUNT(QuizAnswers.QuizProfileID) AS Cnt, SUM(QuizAnswers.AnsweredYes) As TotalScore
, ROW_NUMBER() OVER (ORDER BY TotalScore) AS RowNumber
FROM QuizAnswers INNER JOIN
Quizzes ON QuizAnswers.QuizID = Quizzes.QuizID
WHERE (Quizzes.PartnerID = 16)
GROUP BY QuizAnswers.QuizProfileID
HAVING COUNT(QuizAnswers.QuizProfileID)= 5
)
it should work for your query

Answer 2

Median value of numeric values is often over though. Just use this example:
DECLARE #testTable TABLE
(
VALUE INT
)
--INSERT INTO #testTable -- Even Test
--SELECT 3 UNION ALL
--SELECT 5 UNION ALL
--SELECT 7 UNION ALL
--SELECT 12 UNION ALL
--SELECT 13 UNION ALL
--SELECT 14 UNION ALL
--SELECT 21 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 29 UNION ALL
--SELECT 40 UNION ALL
--SELECT 56
--
--INSERT INTO #testTable -- Odd Test
--SELECT 3 UNION ALL
--SELECT 5 UNION ALL
--SELECT 7 UNION ALL
--SELECT 12 UNION ALL
--SELECT 13 UNION ALL
--SELECT 14 UNION ALL
--SELECT 21 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 23 UNION ALL
--SELECT 29 UNION ALL
--SELECT 39 UNION ALL
--SELECT 40 UNION ALL
--SELECT 56
DECLARE #RowAsc TABLE
(
ID INT IDENTITY,
Amount INT
)
INSERT INTO #RowAsc
SELECT VALUE
FROM #testTable
ORDER BY VALUE ASC
SELECT AVG(amount)
FROM #RowAsc ra
WHERE ra.id IN
(
SELECT ID
FROM #RowAsc
WHERE ra.id -
(
SELECT MAX(id) / 2.0
FROM #RowAsc
) BETWEEN 0 AND 1
)