----------------[change SQL prompt]-----------------
set sqlprompt '_user"> "'

----------------[ change date format ]-------------
alter session set NLS_DATE_FORMAT='yy/mm/dd';
select sysdate from dual;

----------------[ drop tables ]----------------------
select 'drop table '|| Rpad(tname,20) ||' cascade constraints ;' from tab;
select 'purge recyclebin ;' from dual;
----------------------------------------------------