Syntax
------

SOUNDEX(str)

Description
-----------

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 non-alphabetic 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 details:

* 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 reasonable results.

* This function implements the original Soundex algorithm, not the more
popular enhanced version (also described by D. Knuth). The difference is that
original version discards vowels first and duplicates second, whereas the
enhanced version discards duplicates first and vowels second.

Examples
--------

SOUNDEX('Hello');
+------------------+
| SOUNDEX('Hello') |
+------------------+
| H400             |
+------------------+

SELECT SOUNDEX('MariaDB');
+--------------------+
| SOUNDEX('MariaDB') |
+--------------------+
| M631               |
+--------------------+

SELECT SOUNDEX('Knowledgebase');
+--------------------------+
| SOUNDEX('Knowledgebase') |
+--------------------------+
| K543212                  |
+--------------------------+

SELECT givenname, surname FROM users WHERE SOUNDEX(givenname) =
SOUNDEX("robert");
+-----------+---------+
| givenname | surname |
+-----------+---------+
| Roberto   | Castro  |
+-----------+---------+

URL: https://mariadb.com/kb/en/soundex/