CREATE EXTENSION "soundex-function";
-- john and joan should be similar
SELECT soundex('john');
 soundex 
---------
 J500
(1 row)

SELECT soundex('joan');
 soundex 
---------
 J500
(1 row)

-- principally is a longer word
SELECT soundex('principally');
 soundex 
---------
 P652
(1 row)

-- there, their, and they're should match
SELECT soundex('there') = soundex('their')
  AND soundex('they''re') = soundex('there');
 ?column? 
----------
 t
(1 row)