Try this: it should show every row from usys (with the row data - probably some name - you want to show) and the description for those items the user has rights to.
If you want only udesc.description then write ISNULL(udes.description, "NO RIGHTS") - ISNULL is sql server function, in oracle use NVL(udesc.description, "NO RIGHTS")
Both functions will return text NO RIGHTS if udesc.description is NULL (i.e. the user has no rows in udesc.
select usys.some-field, udesc.description
from u_systems_dev usys
LEFT JOIN u_user_systems_dev udesc ON usys.system_id = udesc.id
WHERE
usys.user_id = 'username';
If this helps please take time to accept the solution. Thank you.