各部分をかっこで囲んでください。とにかく、12.2で動作します:
( Select * From tabl1 where Date = '04-MAR-2020' FETCH FIRST 1 ROW )
UNION ALL
( Select * From tabl1 where Date = '05-MAR-2020' FETCH FIRST 1 ROW )
興味のある人のための私の実際のテストクエリはこれでした:
(select object_name
from user_objects
where object_type = 'TABLE'
order by object_name
fetch first 1 row only)
UNION ALL
(select object_name
from user_objects
where object_type = 'VIEW'
order by object_name
fetch first 1 row only);