## Issue

What’s the simplest (and hopefully not too slow) way to calculate the median with MySQL? I’ve used `AVG(x)`

for finding the mean, but I’m having a hard time finding a simple way of calculating the median. For now, I’m returning all the rows to PHP, doing a sort, and then picking the middle row, but surely there must be some simple way of doing it in a single MySQL query.

Example data:

```
id | val
--------
1 4
2 7
3 2
4 2
5 9
6 8
7 3
```

Sorting on `val`

gives `2 2 3 4 7 8 9`

, so the median should be `4`

, versus `SELECT AVG(val)`

which == `5`

.

## Solution

In MariaDB / MySQL:

```
SELECT AVG(dd.val) as median_val
FROM (
SELECT d.val, @rownum:[email protected]+1 as `row_number`, @total_rows:[email protected]
FROM data d, (SELECT @rownum:=0) r
WHERE d.val is NOT NULL
-- put some where clause here
ORDER BY d.val
) as dd
WHERE dd.row_number IN ( FLOOR((@total_rows+1)/2), FLOOR((@total_rows+2)/2) );
```

Steve Cohen points out, that after the first pass, @rownum will contain the total number of rows. This can be used to determine the median, so no second pass or join is needed.

Also `AVG(dd.val)`

and `dd.row_number IN(...)`

is used to correctly produce a median when there are an even number of records. Reasoning:

```
SELECT FLOOR((3+1)/2),FLOOR((3+2)/2); -- when total_rows is 3, avg rows 2 and 2
SELECT FLOOR((4+1)/2),FLOOR((4+2)/2); -- when total_rows is 4, avg rows 2 and 3
```

Finally, MariaDB 10.3.3+ contains a MEDIAN function

Answered By – velcrow

Answer Checked By – Pedro (BugsFixing Volunteer)