What would be the best way to enable the calculation of a median value (assuming a numeric data type) in an aggregate query?

General Discussions
,
#1

According to MSDN (Aggregate Functions (Transact-SQL) - SQL Server | Microsoft Learn), the Median function is unavailable as an aggregate function in Transact-SQL. However, I would like to know if it is possible to create this functionality using the Create Aggregate function, a user-defined function, or another method.

What would be the best way to enable the calculation of a median value (assuming a numeric data type) in an aggregate query?

#2

Hello Anusha,

Using a Common Table Expression (CTE) : A common method to calculate the median in SQL Server is by using a Common Table Expression (CTE) to rank the rows and then select the middle value(s).

WITH SortedValues AS (
    SELECT
        value,
        ROW_NUMBER() OVER (ORDER BY value) AS RowAsc,
        ROW_NUMBER() OVER (ORDER BY value DESC) AS RowDesc
    FROM
        YourTable
)

SELECT
    AVG(value) AS Median
FROM
    SortedValues
WHERE
    RowAsc = RowDesc
    OR RowAsc + 1 = RowDesc
    OR RowAsc = RowDesc + 1;

This CTE ranks the values in ascending and descending order. Main Query: It then selects the middle value(s). If there is an even number of values, it averages the two middle values.

#3

Hey Jacqueline,

Using SQL Server’s PERCENTILE_CONT Function: SQL Server 2012 and later versions include the PERCENTILE_CONT function, which can be used to calculate the median.

SELECT
    PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY value) AS Median
FROM
    YourTable;

  • PERCENTILE_CONT(0.5): This calculates the values’ median (50th percentile) in the specified order.

  • WITHIN GROUP (ORDER BY value): This clause specifies the order of the values for which the percentile is calculated.

I hope this works

#4

Using a User-Defined Function (UDF) : You can create a user-defined function to calculate the median. Here’s an example of creating and using such a function:

CREATE FUNCTION dbo.fnMedian (@ListOfValues FLOAT)
RETURNS FLOAT
AS
BEGIN
    DECLARE @Median FLOAT;
    WITH SortedValues AS (
        SELECT
            value,
            ROW_NUMBER() OVER (ORDER BY value) AS RowAsc,
            ROW_NUMBER() OVER (ORDER BY value DESC) AS RowDesc
        FROM
            @ListOfValues
    )
    SELECT
        @Median = AVG(value)
    FROM
        SortedValues
    WHERE
        RowAsc = RowDesc
        OR RowAsc + 1 = RowDesc
        OR RowAsc = RowDesc + 1;
    
    RETURN @Median;
END
GO

– Using the function

SELECT dbo.fnMedian(value) AS Median
FROM YourTable;

explanation:

Creating the UDF: This function sorts the values and calculates the median using the same logic as in Answer 1. Using the UDF: You can call this function within your queries to calculate the median for any set of values.

I hope I was able to clear your doubt @anusha_gg