Description:
The below script exposes an incorrect result for AVG with the window-frame ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING.

The result is wrong for the second row (it seems to return the SUM, not divided by the count).

Problem does not exists in 8.0.31 or earlier and also not in 8.0.32 when using RANGE instead of ROWS.

How to repeat:
CREATE TABLE t (
    n INTEGER
);

INSERT INTO t VALUES (1), (2), (3), (4);

SELECT n
     , SUM(n)   OVER(ORDER BY n ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) AS "sum(n)"
     , COUNT(*) OVER(ORDER BY n ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) AS "count(n)"
     , AVG(n)   OVER(ORDER BY n ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) AS "avg(n)"
     , SUM(n)   OVER(ORDER BY n ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING)
     / COUNT(*) OVER(ORDER BY n ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) AS "sum(n)/count(n)"
  FROM t
 ORDER BY n;

+------+--------+----------+--------+-----------------+
| n    | sum(n) | count(n) | avg(n) | sum(n)/count(n) |
+------+--------+----------+--------+-----------------+
|    1 |      9 |        3 | 3.0000 |          3.0000 |
|    2 |      7 |        2 | 7.0000 |          3.5000 | <-- Column "avg(n)" is wrong.
|    3 |      4 |        1 | 4.0000 |          4.0000 |
|    4 |   NULL |        0 |   NULL |            NULL |
+------+--------+----------+--------+-----------------+

Hello Markus,

Thank you for the report and test case.
Verified as described.

regards,
Umesh

Documented fix as follows in the MySQL 8.0.33 changelog:

    AVG(...) OVER (ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) did not
    return the correct result.

Closed.