Hello Raymond and others,
thank you for looking at my problem!
It is a core Drupal 7 table, with a prefix "drupal_"
(you can set it while installing Drupal 7 in adv. options).
I have only 2 records in that target table:
# select uid, name, mail, created, access from drupal_users;
uid | name | mail | created | access
-----+------+----------------------------+------------+------------
0 | | | 0 | 0
1 | Alex | Alexander.Farber@gmail.com | 1299512207 | 1299753672
(2 rows)
I've tried you suggestion and the conflicting record is 'Alex':
# select username, user_id from phpbb_users where exists
(select 1 from drupal_users
where drupal_users.name = phpbb_users.username);
username | user_id
----------+---------
Alex | 2
(1 row)
But isn't that record excluded by the conditions below?
# INSERT INTO drupal_users (uid, name, mail, created, access)
SELECT user_id, username, user_email, user_regdate, user_lastvisit
FROM phpbb_users
WHERE user_id > 50 and length(username) > 0 and username <> 'Alex';
ERROR: duplicate key value violates unique constraint "drupal_users_name_key"