Although the standard soundex string is 4 characters long, and this is what's returned by the php function, some database programs return an arbitrary number of strings. MySQL, for instance.
The MySQL documentation covers this, recommending that you may wish to use substring to output the standard 4 characters. Let's take 'Dostoyevski' as an example.
select soundex("Dostoyevski")
returns D2312
select substring(soundex("Dostoyevski"), 1, 4);
returns D231
PHP will return the value as 'D231'
So, to use the soundex function to generate a WHERE parameter in a MySQL SELECT statement, you might try this:
$s = soundex('Dostoyevski');
SELECT * FROM authors WHERE substring(soundex(lastname), 1 , 4) = "' . $s . '"';
Or, if you want to bypass the php function
$result = mysql_query("select soundex('Dostoyevski')");
$s = mysql_result($result, 0, 0);
