By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
select NVL(NULL, 'A'),
NVL('', 'A'),
COALESCE(NULL, 'A'),
COALESCE('', 'A')
from dual
| NVL(NULL,'A') | NVL('','A') | COALESCE(NULL,'A') | COALESCE('','A') |
|---|---|---|---|
| A | A | A | A |