label_query.sql

WITH
val (l_name,d_label ) AS
 (values
     (? , ?)
 ),
ins AS
 ( INSERT INTO
     label (label_name, device_label)
   SELECT l_name, d_label FROM val
   ON CONFLICT ON CONSTRAINT label_name_unique DO NOTHING
   RETURNING id ,label_name               -- only the inserted ones
 )
SELECT COALESCE(ins.id, label.id) AS id
FROM val
LEFT JOIN ins ON ins.label_name = val.l_name
LEFT JOIN label ON label.label_name = val.l_name ;