If Oracle SQL queries don't return a result (zero rows) subsequent jobs fail as there is no output to write, even though the query ran succesfully. For example creation of an Excel file based on the output of the query will fail, unless you build in logic to prevent this.

You can test if there is no output, but it would be nicer to - on request - get something back as in SQL*Plus, as "# of row(s) selected".