How to select median value? [duplicate] - mysql

Question

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Simple way to calculate median with MySQL
(48 answers)
Closed 4 years ago.
Could anybody give me a hint how to find median value for "tax" during 12.04.18 - 16.04.18:
user_id login_time tax
3 2018-04-15 16625000
5 2018-04-16
6 2018-04-17 296470000
6 2018-04-16 192519750
6 2018-04-15 4455500
6 2018-04-13 17125
6 2018-04-12 120180000
7 2018-04-18 24060000
7 2018-04-17 42959500
The result equals 16625000 (because there is NULL value. We need to use it as 0).
Thank U for attention to my question!

Answer 1

The median is the value
located exactly in the middle of an odd dataset.
Or the average of the two middle values in an even dataset.
So, by considering this two cases, the first you need is the count of datarows. Then, you have to decide (simple case) if you pick the value in the middle, or if you need the average of two values (Don't forget to apply sorting prior to selecting the actual values):
I would use a little "code" to achieve this:
Pseudo-Code:
1.) SELECT count(id) AS val FROM myTable WHERE datetime ... //$val=9
2.) Programming language: $lim = floor($val/2); // $lim=4
if odd($val){
3.) SELECT tax FROM myTable WHERE datetime [...] ORDER BY tax LIMIT $lim,1
}
else if even($val){
3.) Programming language: $lim -=1; // if $val was 10, we want row 4 and 5
4.) SELECT AVG(tax) AS tax FROM
(SELECT * FROM myTable WHERE datetime [...] ORDER BY tax LIMIT $lim,2) AS tmp
}
[...]
echo "Median is: ". $row["tax"];