How to perform Soundex encoding on a given string using the SOUNDEX() function?

SOUNDEX(str) is a MySQL built-in function that returns the Soundex coding of a given string. Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. For example:

SELECT SOUNDEX('Sophia'), SOUNDEX('Sofia');
  -- +-------------------+------------------+
  -- | SOUNDEX('Sophia') | SOUNDEX('Sofia') |
  -- +-------------------+------------------+
  -- | S100              | S100             |
  -- +-------------------+------------------+

Reference information of the SOUNDEX() function:

SOUNDEX(str): code
  Returns a soundex string from str, or NULL if str is NULL. Two strings
  that sound almost the same should have identical soundex strings.

Arguments, return value and availability:
  str: Required. The string that will be Soundex encoded from.
  code: Return value. The Soundex code of the given string.
  Available since MySQL 5.7.

⇒ SPACE() - Repeating Space Character

⇐ RTRIM() - Right-Trimming String

⇑ MySQL Functions on Character String Values

⇑⇑ MySQL Function References