Calculate Median in MySQL

Median :
In statistics and probability theory, Median is a value separating the higher half from the lower half of a data sample, a population, or a probability distribution. In lay-man language, Median is the middle value of a sorted listed of values.

Calculate Median value in MySQL –
Consider a table demo where Name is the student name and Distance is the total distance (in km) from their home to college.

Name	Distance
Sumit	25
Jaskirat	35
Sukrut	20
Shivam	20
Sanchit	45
Prince	35
Keshav	15
Preet	25
Saurav	20

We calculate the median of the Distance from the demo table.
Query –

SET @rowindex := -1;
 
SELECT
   AVG(d.distance) as Median 
FROM
   (SELECT @rowindex:=@rowindex + 1 AS rowindex,
           demo.distance AS distance
    FROM demo
    ORDER BY demo.distance) AS d
WHERE
d.rowindex IN (FLOOR(@rowindex / 2), CEIL(@rowindex / 2));

Explanation :

1. Beginning with the internal subquery – the select assigns @rowindex as an incremental index for each distance that is selected and sorts the distance.
2. Once we have the sorted list of distances, the outer query will fetch the middle items in the array. If the array contains an odd number of items, both values will be the single middle value.
3. Then, the SELECT clause of the outer query returns the average of those two values as the median value.

Output –

25.0000

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