Updated: 31 Oct 2012

Use RunningDEVSQ to calculate the sum of squares of deviations of column values from their sample mean in an ordered resultant table, without the need for a self-join. The sum of squares of deviations 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].[RunningDEVSQ](

<@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 RunningDEVSQ calculation. *@Id* allows you to specify multiple RunningDEVSQ 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 sum of squares deviation, use the MovingDEVSQ function.

· If *@RowNum* is equal to 1, RunningDEVSQ is equal to 0.

· *@RowNum* must be in ascending order.

· To calculate a single sum of squares deviation for a set of data, use the DEVSQ function.

· 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 sample data from a population with a mean of 100 and a standard deviation of 15.

SELECT rn

,x

,wct.RunningDEVSQ(x,rn,NULL) as [DEVSQ]

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 DEVSQ

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

1 85.2968 0

2 88.2566 4.38020802000028

3 100.1934 124.385433946668

4 116.3052 595.247808399996

5 109.6867 713.806985752005

6 130.3847 1485.81409745335

7 76.5458 2180.79610035717

8 99.5511 2182.51512771877

9 101.5546 2183.05186205559

10 114.3180 2345.96392634903

11 100.2686 2349.38781514546

12 110.5982 2416.63905324921

13 91.4181 2535.10292059694

14 118.5804 2794.23302841429

15 126.6649 3313.90629879603

16 103.8977 3314.42501562004

17 82.2819 3783.01481601768

18 123.3369 4162.85005420446

19 98.9415 4191.0424129611

20 89.1731 4402.98455185802