How to count the number of bytes of a giving string using the LENGTH() function?

LENGTH(string) is a MySQL built-in function that returns the number of bytes of a giving string. For example:

SET @string = 'Bonjour Françoise';

SELECT LENGTH(@string), CHAR_LENGTH(@string);
  -- +-----------------+----------------------+
  -- | LENGTH(@string) | CHAR_LENGTH(@string) |
  -- +-----------------+----------------------+
  -- |              18 |                   17 |
  -- +-----------------+----------------------+

SELECT LENGTH('O'), LENGTH('©'), LENGTH('😋');
  -- +-------------+--------------+----------------+
  -- | LENGTH('O') | LENGTH('©')  | LENGTH('😋')     |
  -- +-------------+--------------+----------------+
  -- |           1 |            2 |              4 |
  -- +-------------+--------------+----------------+

SELECT HEX('O'), HEX('©'), HEX('😋');
  -- +----------+-----------+-------------+
  -- | HEX('O') | HEX('©')  | HEX('😋')     |
  -- +----------+-----------+-------------+
  -- | 4F       | C2A9      | F09F988B    |
  -- +----------+-----------+-------------+

Reference information of the LENGTH() function:

LENGTH(str): num
  Returns the length of the string str, measured in bytes. A multibyte
  character counts as multiple bytes. This means that for a string
  containing five 2-byte characters, LENGTH() returns 10, whereas
  CHAR_LENGTH() returns 5. Returns NULL if str is NULL.

Arguments, return value and availability:
  str: Required. The given string to count the number of bytes for.
  num: Return value. The number of bytes in the given string.
  Available since MySQL 4.0.

Related MySQL functions:

• CHARACTER_LENGTH() - Number of Characters
• CHAR_LENGTH() - Number of Characters
• LENGTH() - Number of Bytes in String
• BIT_LENGTH() - Number of Bits in String

⇒ LOCATE() - Locate Substring Starting at N

⇐ LEFT() - First N Characters

⇑ MySQL Functions on Character String Values

⇑⇑ MySQL Function References