INSERT ... SELECT DISTINCT - Doesn't work...

Hi

I'm trying to normalize a database, and want to derivate one relation
from another. The original relation is like:

user_operations (
user_id integer,
user_name varchar,
user_operation varchar)

It stores the 'user_operation' item, and also works as a user database
(or some like this...). To get the different users from the database, I
have this query:

SELECT DISTINCT user_id, user_name FROM user_operations;

I need to do some normalization works here, and want to insert data from
user_operations in the new 'users' relation:

CREATE TABLE users (
user_id integer,
user_name varchar);

To inser the data, I have tried the straight:

INSERT
INTO users (user_id, user_name)
SELECT DISTINCT user_id, user_name FROM user_operations;

But it doesn't work as I expect. Suppose there are 15000 rows at
user_operations, but only 50 different (user_id, user_name). The SELECT
DISTINCT returns only 50 rows, but the INSERT ... SELECT DISTINCT
inserts 15000 rows!

I think the DISTINCT clause, when used in a INSERT INTO ... SELECT
doesn't have any effect... Is it a bug?

Can anybody help me figure out how to get only the different (user_id,
user_name) from user_operations, without any repeat?

TIA
--
César A. K. Grossmann
ckant(at)usa(dot)net
http://members.xoom.com/ckant/
http://www.halcyon.com/sciclub/cgi-pvt/instr/instr.html