SQL Query For Displaying 'No Data Found' for values containing null and 0 along with other records
An example with CASE statement:

select
  ename, sal, job,
  case
    when comm is null or comm = 0 then 'No data found'
    else to_char(comm)
  end as comm
from
  emp
;


The UNION [ALL], INTERSECT, MINUS Operators


  The corresponding expressions in the select lists of the component queries of a compound query must match in number and must be in the same data type group (such as numeric or character).