SQLite soundex string length

Question

Does soundex function in sqlite has limitation on string length? As I found that the result of

SELECT soundex('Schneider Thomson'), soundex('Schneider Rene'), soundex('Schneider')

Are all the same value which equal S536, However the result of :

SELECT soundex('Schn Thomson'), soundex('Schn Rene'), soundex('Schn');

Is different for each string and the values is

soundex('Schn Thomson') = S535 
soundex('Schn Rene')    = S565
soundex('Schn')         = S500

Please can any one explain why?

Answer 1

The Soundex algorithm is desgined to work on single words. (To simplify, it encodes the first letter and the first three following consonants.)

Answer 2

To provide a little more clarification to CL's answer, the encoding uses the first letter and then encodes the following consonants (with the exception of H,W,Y) until 3 digits have been generated. Mississippi is a word that illustrates this well. MISSISSIPPI has a SOUNDEX of M210.

1. M is the first letter followed by the first consonant S. S is then repeated and ignored by SOUNDEX encoding.
2. The next consonant is P and it is not followed by another valid letter (just a repeated p and an i).
3. Thus a zero is the final digit.

Hopefully that provides a little more clarification on how SOUNDEX encodes words. For a little more information, this article from Genealogy.com explains how to use SOUNDEX when researching names. This would explain why supercell and supercalifragilisticexpialidocious have the same SOUNDEX, S162.