test=# ALTER ROLE user1 RESOURCE GROUP NONE;
NOTICE:  resource group required -- using default resource group "default_group"
ALTER ROLE
tpch1s=# SELECT rolname, rsgname FROM pg_roles, pg_resgroup WHERE pg_roles.rolresgroup=pg_resgroup.oid;
 rolname |   rsgname   
---------+-------------
 gpadmin | admin_group
 user1   | default_group
(2 rows)