Syntax:
SOUNDEX(str)

Returns a soundex string from str. Two strings that sound almost the
same should have identical soundex strings. A standard soundex string
is four characters long, but the SOUNDEX() function returns an
arbitrarily long string. You can use SUBSTRING() on the result to get a
standard soundex string. All nonalphabetic characters in str are
ignored. All international alphabetic characters outside the A-Z range
are treated as vowels.

*Important*: When using SOUNDEX(), you should be aware of the following
limitations:

o This function, as currently implemented, is intended to work well
  with strings that are in the English language only. Strings in other
  languages may not produce reliable results.

o This function is not guaranteed to provide consistent results with
  strings that use multibyte character sets, including utf-8.

  We hope to remove these limitations in a future release. See Bug
  #22638 for more information.

URL: http://dev.mysql.com/doc/refman/5.7/en/string-functions.html

