[sqlite] writing simple or aggregate user function

[Marcel Strittmatter]

Hi all,
I have a similar setup like the following:
  CRETAE TABLE users (id int primary key, name varchar(30));
  INSERT INTO users VALUES (1, 'john');
  INSERT INTO users VALUES (2, 'frank');
  INSERT INTO users VALUES (3, 'david');
  CREATE TABLE groups (id int primary key, name varchar(20), users_ids 
varchar(100));
  INSERT INTO groups VALUES (1, 'group 1', '1,2,3');

The field 'users_ids' in the table 'groups' holds the primary keys of 
related users (I know that there are better ways to design such a 
relation), but I like to do the following select statement without 
joining tables and grouping...

SELECT name, user_list(users_ids) from groups;
should return => 'group 1', 'john, frank, david'
I now like to create the user function user_list(), but I didn't find 
out how to execute a select query inside this user function. Is this 
possible without locking the database out? Where do I get the database 
pointer from the already opened database?

Is it possible to create a simple user function that does this?
If it is more easy to get the desired result if I create a relation 
table between users and groups and use an aggregate function?

Thanks for any suggestions and help
Marcel