Fill select boxes with dependent data from a database. How?

Hi all, i am searching for a solution for filling 2 (or 3) dependent select boxes with values from a database. That means, when you select a value in selectbox 1 the options for the second selectbox should be filled with values related to select box 1. Short example Value for box 1 Value for box 2 1 a 1 b 1 c 2 d 2 e 2 f If you now select "1" in select box 1 then you should only see "a","b" and "c" in selectbox 2. Was that clear? I hope so. Does anybody has a solution for this situation? Or maybe sample code? Thank you in advance for any help. Kind regards and greetings from Cologne/Germany, Marco. mviehl@gmx.de