SQL Server RunningAVG Function

Updated 2023-11-14 13:44:51.573000

Description

Use the scalar function RunningAVG to calculate the average of column values in an ordered resultant table, without having to do a self-join. The average value is calculated for each value 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.

Syntax

SELECT [westclintech].[wct].[RunningAVG] (
  <@Val, float,>
 ,<@RowNum, int,>
 ,<@Id, tinyint,>)

Arguments

@Val

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

@RowNum

the number of the row within the group for which the average 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.

@Id

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

Return Type

float

Remarks

If @Id is NULL then @Id = 0.

To calculate moving averages, use the MovingAVG function.

To calculate moving averages for time series, use the DEMA or DWMA function.

If @RowNum is equal to 1, RunningAVG is equal to @Val.

@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.

Examples

In this example we will calculate the average check amount in a check register from the first check to the last check. We will create a temporary table, #c, populate it with some data and then run the SELECT.

/*Create the temporary table*/
CREATE TABLE #c
(
    num_check int,
    date_check datetime,
    payee varchar(50),
    amt_check money,
    Primary Key (num_check)
);
/*Populate the table with some data*/
INSERT INTO #c
VALUES
(1200, '2012-01-31', 'Gas Company', 108.49);
INSERT INTO #c
VALUES
(1201, '2012-01-31', 'Electric Company', 98.27);
INSERT INTO #c
VALUES
(1202, '2012-01-31', 'Telephone Company', 136.6);
INSERT INTO #c
VALUES
(1203, '2012-01-31', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1204, '2012-01-31', 'Mortgage Bank', 1129.23);
INSERT INTO #c
VALUES
(1205, '2012-02-29', 'Gas Company', 153.89);
INSERT INTO #c
VALUES
(1206, '2012-02-29', 'Electric Company', 121.99);
INSERT INTO #c
VALUES
(1207, '2012-02-29', 'Telephone Company', 138.92);
INSERT INTO #c
VALUES
(1208, '2012-02-29', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1209, '2012-02-29', 'Mortgage Bank', 1129.23);
INSERT INTO #c
VALUES
(1210, '2012-03-31', 'Gas Company', 70.79);
INSERT INTO #c
VALUES
(1211, '2012-03-31', 'Electric Company', 93.57);
INSERT INTO #c
VALUES
(1212, '2012-03-31', 'Telephone Company', 149.78);
INSERT INTO #c
VALUES
(1213, '2012-03-31', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1214, '2012-03-31', 'Mortgage Bank', 1129.23);
INSERT INTO #c
VALUES
(1215, '2012-04-30', 'Gas Company', 105.58);
INSERT INTO #c
VALUES
(1216, '2012-04-30', 'Electric Company', 149.36);
INSERT INTO #c
VALUES
(1217, '2012-04-30', 'Telephone Company', 145.35);
INSERT INTO #c
VALUES
(1218, '2012-04-30', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1219, '2012-04-30', 'Mortgage Bank', 1129.23);
INSERT INTO #c
VALUES
(1220, '2012-05-31', 'Gas Company', 96.27);
INSERT INTO #c
VALUES
(1221, '2012-05-31', 'Electric Company', 114.62);
INSERT INTO #c
VALUES
(1222, '2012-05-31', 'Telephone Company', 145.43);
INSERT INTO #c
VALUES
(1223, '2012-05-31', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1224, '2012-05-31', 'Mortgage Bank', 1129.23);
INSERT INTO #c
VALUES
(1225, '2012-06-30', 'Gas Company', 147.03);
INSERT INTO #c
VALUES
(1226, '2012-06-30', 'Electric Company', 130.52);
INSERT INTO #c
VALUES
(1227, '2012-06-30', 'Telephone Company', 147.71);
INSERT INTO #c
VALUES
(1228, '2012-06-30', 'Car Leasing Company', 361.75);
INSERT INTO #c
VALUES
(1229, '2012-06-30', 'Mortgage Bank', 1129.23);
/*Calculate the running average*/
SELECT num_check,
       cast(convert(varchar, date_check, 106) as char(11)) as date_check,
       cast(payee as char(20)) as payee,
       amt_check,
       wct.RunningAvg(amt_check, num_check, NULL) as [Running AVG]
FROM #c;

This produces the following result.

In this example, we calculate the average by payee in date order and use the ROW_NUMBER() function to determine the @RowNum value passed into the RunningAVG function.

SELECT num_check,
       cast(convert(varchar, date_check, 106) as char(11)) as date_check,
       cast(payee as char(20)) as payee,
       amt_check,
       wct.RunningAvg(amt_check, ROW_NUMBER() OVER (PARTITION BY payee ORDER BY 
                 payee, num_check), NULL) as [Running AVG]
FROM #c
ORDER BY payee,
         num_check;

This produces the following result.

In this example we calculate 2 running averages which we will call the month-to-date (MTD) running average and the year-to-date (YTD) running average.

SELECT num_check as [check],
       cast(convert(varchar, date_check, 106) as char(11)) as date_check,
       cast(payee as char(20)) as payee,
       amt_check,
       ROUND(wct.RunningAvg(amt_check, ROW_NUMBER() OVER (PARTITION BY MONTH(
                 date_check)ORDER BY num_check), 1), 2) as [MTD AVG],
       ROUND(wct.RunningAvg(amt_check, num_check, NULL), 2) as [YTD AVG]
FROM #c
ORDER BY num_check;

This produces the following result.