问如何在连接可能为空的字段时返回替代连接？

EN

SELECT last_name
  ||
  CASE
    WHEN last_name IS NULL
    OR first_name  IS NULL
    THEN NULL
    ELSE ', '
  END
  || first_name
FROM <your table>

   SELECT last_name
      ||
      CASE CONCAT(first_name , person_name) as fullname
      WHEN NULL
      THEN NULL
      ELSE 
      CONCAT(',',fullname)
      END
    from ...

select nvl2(last_name, first_name||', '||last_name, first_name) as person_name
from   ...;