SQL ERROR [ postgres ]

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list []

SQL

SELECT DISTINCT u.user_id, u.username FROM phpbb_users u, phpbb_acl_users a WHERE u.user_id = a.user_id AND a.forum_id IN (1, 2) AND (a.auth_option_id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30) OR a.auth_role_id IN (14, 15, 16, 17, 18, 19, 20, 21, 22)) ORDER BY u.username_clean, u.user_regdate ASC

BACKTRACE

FILE: includes/db/postgres.php

LINE: 177

CALL: dbal->sql_error()

FILE: includes/acp/acp_permissions.php

LINE: 1165

CALL: dbal_postgres->sql_query()

FILE: includes/acp/acp_permissions.php

LINE: 399

CALL: acp_permissions->retrieve_defined_user_groups()

FILE: includes/functions_module.php

LINE: 471

CALL: acp_permissions->main()

FILE: adm/index.php

LINE: 74

CALL: p_master->load_active()