How to calculate the average value of a field expression in result set groups using the ANY_VALUE() function?

ANY_VALUE(expr) is a MySQL built-in aggregate function that returns any value of a field expression in result set groups. For example:

SELECT help_category_id, MAX(Name), ANY_VALUE(Name)
  FROM mysql.help_topic GROUP BY help_category_id;
  -- +------------------+-----------------------------------+---------------------+
  -- | help_category_id | MAX(Name)                         | ANY_VALUE(Name)     |
  -- +------------------+-----------------------------------+---------------------+
  -- |                1 | HELP_VERSION                      | HELP_DATE           |
  -- |                2 | YEAR DATA TYPE                    | AUTO_INCREMENT      |
  -- |                3 | SHUTDOWN                          | HELP COMMAND        |
  -- |                4 | TRUE                              | TRUE                |
  -- |                5 | SPATIAL INDEXES                   | GEOMETRY HIERARCHY  |
  -- ...
  -- +------------------+-----------------------------------+---------------------+

SELECT help_category_id, MAX(help_topic_id), ANY_VALUE(2*help_topic_id)
  FROM mysql.help_topic GROUP BY help_category_id;
  -- +------------------+--------------------+----------------------------+
  -- | help_category_id | MAX(help_topic_id) | ANY_VALUE(2*help_topic_id) |
  -- +------------------+--------------------+----------------------------+
  -- |                1 |                  1 |                          0 |
  -- |                2 |                 39 |                          4 |
  -- |                3 |                675 |                          6 |
  -- |                4 |                  5 |                          8 |
  -- |                5 |                 44 |                         80 |
  -- ...
  -- +------------------+--------------------+----------------------------+

Reference information of the ANY_VALUE() function:

ANY_VALUE(expr): any
  Returns a randomly selected value of expr from each result set group.

Arguments, return value and availability:
  expr: Required. The field expression in result set groups.
  any: Return value. An any value of the input expression.
  Available since MySQL 5.7.

⇒ AVG() - Average Value in Group

⇐ MySQL Functions on Aggregation Groups

⇑ MySQL Functions on Aggregation Groups

⇑⇑ MySQL Function References