SQL query

[jovery]

Adjust you query as follows:

declare
  cursor c1 is select table_name from dba_tables where owner='TROPP' ;
  tname varchar2(30000):= null ;
begin
  for i in c1
    loop
      tname:= tname||i.table_name||',';
    end loop;
  dbms_output.put_line(tname);
end;

However, you will need to put a loop in to keep the output line below 256 characters which is the maximum for dbms_output.put_line

HTH