How to obtain the first value of a field expression in the current result set window using the FIRST_VALUE() function?

FIRST_VALUE(exp) is a MySQL built-in window function that returns the first value of a field expression in the current result set window. For example:

SELECT help_topic_id AS tip, help_category_id AS cid,
  name, FIRST_VALUE(name) OVER w
  FROM mysql.help_topic
  WINDOW w AS (PARTITION BY help_category_id);
  -- +-----+-----+----------------+--------------------------+
  -- | tip | cid | name           | FIRST_VALUE(name) OVER w |
  -- +-----+-----+----------------+--------------------------+
  -- |   0 |   1 | HELP_DATE      | HELP_DATE                |
  -- |   1 |   1 | HELP_VERSION   | HELP_DATE                |
  -- |   2 |   2 | AUTO_INCREMENT | AUTO_INCREMENT           |
  -- |   6 |   2 | BIT            | AUTO_INCREMENT           |
  -- |   7 |   2 | TINYINT        | AUTO_INCREMENT           |
  -- |   8 |   2 | BOOLEAN        | AUTO_INCREMENT           |
  -- |   9 |   2 | SMALLINT       | AUTO_INCREMENT           |
  -- ...
  -- +-----+-----+----------------+--------------------------+

Reference information of the FIRST_VALUE() function:

FIRST_VALUE(exp): val
  Returns the first value of a field expression
  in the current result set window.

Arguments, return value and availability:
  exp: Required. The field expression to be evaluated.
  val: Return value. The first value of exp in the current window.
  Available since MySQL 8.

Related MySQL functions:

• FIRST_VALUE() - First Value of Result Set Window
• LAST_VALUE() - Last Value of Result Set Window
• NTH_VALUE() - N-th Value of Result Set Window

⇒ LAG() - N-Row before Current Row within Window

⇐ DENSE_RANK() - Density Rank of Sorted Values

⇑ MySQL Functions on Result Set Windows

⇑⇑ MySQL Function References