select to_char('aaa')from dual; select '' || to_char('aaa') || ''from dual; select '''' || to_char('aaa') || '''' from dual; select '''''' || to_char('aaa') || '''''' from dual; select '''''''' || to_char('aaa') || '''''''' from dual; select ' '' ' ||' ' || ' '' ' || to_char('aaa') || ' '' '' ' from dual;