Vensters gebruiken voor statistiek berekenen

SQL Server voor gevorderden

Ginger Grant

Instructor

De standaarddeviatie berekenen

Bereken de standaarddeviatie voor de hele tabel of per venster
STDEV() berekent de standaarddeviatie

Standaarddeviatie voor de hele tabel berekenen

SELECT SalesPerson, SalesYear, CurrentQuota, 
       STDEV(CurrentQuota) 
       OVER () AS StandardDev, 
       ModifiedDate  AS ModDate
FROM SaleGoal

+------------+----------+------------+-----------------+----------+
|SalesPerson |SalesYear |CurrentQuota|StandardDev      | ModDate  |
+------------+----------+------------+-----------------+----------+
|Bob         |2011      |28000.00    |267841.370964233 |2011-04-16|
|Bob         |2011      |7000.00     |267841.370964233 |2011-07-17| 
|Bob         |2011      |91000.00    |267841.370964233 |2011-10-17|
|Bob         |2012      |140000.00   |267841.370964233 |2012-01-15|
|Bob         |2012      |70000.00    |267841.370964233 |2012-04-15|
...
+------------+----------+------------+-----------------+----------+

Standaarddeviatie per partitie berekenen

SELECT SalesPerson, SalesYear, CurrentQuota,  
       STDEV(CurrentQuota) 
       OVER (PARTITION BY SalesYear ORDER BY SalesYear) AS StDev, 
       ModifiedDate AS ModDate
FROM SaleGoal

+------------+----------+------------+-------------+----------+
|SalesPerson |SalesYear |CurrentQuota|StDev        | ModDate  |
+------------+----------+------------+-------------+----------+
|Bob         |2011      |28000.00    |267841.54080 |2011-04-16|
|Bob         |2011      |7000.00     |267841.54080 |2011-07-17| 
|Mary        |2011      |91000.00    |267841.54080 |2011-04-16|
|Mary        |2011      |140000.00   |267841.54080 |2011-07-15|
|Bob         |2012      |70000.00    |246538.86248 |2012-01-15|
|Bob         |2012      |154000.00   |246538.86248 |2012-04-15|
|Bob         |2012      |107000.00   |246538.86248 |2012-07-16|
...
+------------+----------+------------+------------+-----------+

De modus berekenen

De modus is de waarde die het vaakst voorkomt
Modus berekenen:
- Maak een CTE met een geordende telling via ROW_NUMBER
- Gebruik de CTE om de waarde met het hoogste rijnummer te kiezen

De modus berekenen in T-SQL (I)

WITH QuotaCount AS (
SELECT SalesPerson, SalesYear, CurrentQuota,  
       ROW_NUMBER() 
       OVER (PARTITION BY CurrentQuota ORDER BY CurrentQuota) AS QuotaList
FROM SaleGoal 
)
SELECT * FROM QuotaCount

+------------+----------+------------+-------------+
|SalesPerson |SalesYear |CurrentQuota|QuotaList    | 
+------------+----------+------------+-------------+
|Bob         |2011      |7000.00     |1            |
|Bob         |2011      |28000.00    |1            | 
|Bob         |2011      |70000.00    |1            |
|Bob         |2012      |70000.00    |2            |
|Mary        |2012      |73000.00    |1            |
...
+------------+----------+------------+-------------+

Let op: er zijn twee waarden voor 70.000,00

De modus berekenen in T-SQL (II)

WITH QuotaCount AS (
SELECT SalesPerson, SalesYear, CurrentQuota, 
       ROW_NUMBER() 
       OVER (PARTITION BY CurrentQuota ORDER BY CurrentQuota) AS QuotaList
FROM SaleGoal 
)

SELECT CurrentQuota, QuotaList AS Mode 
FROM QuotaCount 
WHERE QuotaList IN (SELECT  MAX(QuotaList) FROM QuotaCount)

+------------+----------+
|CurrentQuota|Mode      | 
+------------+----------+
|70000.00    |2         |
+------------+----------+

Laten we oefenen!

SQL Server voor gevorderden