Updated: 31 Oct 2012

Use RunningVARP to calculate the population variance of column values in an ordered resultant table, without the need for a self-join. The population variance is calculated over all the values from the first value to the last value in the ordered group or partition. If the column values are presented to the functions out of order, an error message will be generated.

SELECT [Example].[wct].[RunningVARP](

<@Val, float,>

,<@RowNum, int,>

,<@Id, tinyint,>)

GO

the value passed into the function. *@Val* is an expression of type **float** or of a type that can be implicitly converted to **float**.

the number of the row within the group for which the sum is being calculated. If *@RowNum* for the current row in a set is less than or equal to the previous *@RowNum* and *@RowNum* is not equal to 1, an error message will be generated.* @RowNum* is an expression of type **int** or of a type that can be implicitly converted to **int**.

a unique identifier for the RunningVARP calculation. *@Id* allows you to specify multiple RunningVARP calculations within a resultant table. *@Id* is an expression of type **tinyint** or of a type that can be implicitly converted to **tinyint**.

· If *@Id* is NULL then *@Id* = 0.

· To calculate moving variances, use the MovingVARP function.

· If *@RowNum* is equal to 1, RunningVARP is equal to zero.

· *@RowNum* must be in ascending order.

· There may be cases where the order in which the data are returned to the function and the order in which the results are returned are different, generally due to parallelism. You can use OPTION(MAXDOP 1) or OPTION(MAXDOP 1,FORCE ORDER) to help eliminate this problem

In this example, we have 20 rows of population data.

SELECT rn

,x

,wct.RunningVARP(x,rn,NULL) as [VARP]

FROM (

SELECT 1,85.2968 UNION ALL

SELECT 2,88.2566 UNION ALL

SELECT 3,100.1934 UNION ALL

SELECT 4,116.3052 UNION ALL

SELECT 5,109.6867 UNION ALL

SELECT 6,130.3847 UNION ALL

SELECT 7,76.5458 UNION ALL

SELECT 8,99.5511 UNION ALL

SELECT 9,101.5546 UNION ALL

SELECT 10,114.318 UNION ALL

SELECT 11,100.2686 UNION ALL

SELECT 12,110.5982 UNION ALL

SELECT 13,91.4181 UNION ALL

SELECT 14,118.5804 UNION ALL

SELECT 15,126.6649 UNION ALL

SELECT 16,103.8977 UNION ALL

SELECT 17,82.2819 UNION ALL

SELECT 18,123.3369 UNION ALL

SELECT 19,98.9415 UNION ALL

SELECT 20,89.1731

) s(rn,x)

This produces the following result.

rn x VARP

----------- --------------------------------------- ----------------------

1 85.2968 0

2 88.2566 2.19010401

3 100.1934 41.4618113155555

4 116.3052 148.8119521

5 109.6867 142.7613971504

6 130.3847 247.635682908889

7 76.5458 311.54230005102

8 99.5511 272.814390964844

9 101.5546 242.561318006173

10 114.3180 234.5963926349

11 100.2686 213.580710467769

12 110.5982 201.386587770764

13 91.4181 195.007916968994

14 118.5804 199.588073458163

15 126.6649 220.9270865864

16 103.8977 207.15156347625

17 82.2819 222.530283295156

18 123.3369 231.269447455802

19 98.9415 220.581179629529

20 89.1731 220.1492275929