MySQL 8.0

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CREATE TABLE sourcetable (id INT, price INT, volume INT)
INSERT INTO sourcetable
WITH RECURSIVE
cte AS ( SELECT 1 price, 1 volume
         UNION ALL
         SELECT price+1, price*price FROM cte WHERE price < 10 )
SELECT price, price, volume
FROM cte
SELECT * 
FROM sourcetable


id
price
volume


1
1
1

2
2
1

3
3
4

4
4
9

5
5
16

6
6
25

7
7
36

8
8
49

9
9
64

10
10
81


WITH cte AS ( SELECT price, SUM(volume) OVER (ORDER BY price ASC) summ 
              FROM sourcetable )
SELECT * 
FROM cte
ORDER BY price
-- total = 286
-- records below 10% = 28.6 are 1..4
-- their average price = 2.5


price
summ


1
1

2
2

3
6

4
15

5
31

6
56

7
92

8
141

9
205

10
286


WITH cte AS ( SELECT price, SUM(volume) OVER (ORDER BY price ASC) summ 
              FROM sourcetable )
SELECT AVG(price)
FROM cte
WHERE summ <= 0.1 * ( SELECT MAX(summ)
                      FROM cte )


AVG(price)


2.5000


WITH cte AS ( 
  SELECT 
    price, 
    SUM(volume) OVER (ORDER BY price ASC) running, 
    SUM(volume) OVER (ORDER BY price ASC 
                      RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) total 
  FROM sourcetable )
SELECT AVG(price)
FROM cte
WHERE running <= 0.1 * total


AVG(price)


2.5000