http://www.oracle.com/technetwork/issue-archive/2011/11-mar/o21plsql-242570.html
http://www.zentut.com/plsql-tutorial/plsql-block-structure/

set serveroutput on;
begin
  dbms_output.put_line ('Hello World!');
end;


declare
    my_var long;
begin
    for x in ( select X from t )
    loop my_var := dbms_lob.substr( x.X, 32000, 1 );