oracle jobs interval

不用case也能半小時refresh一次 :

trunc(sysdate,'HH')+3/1440+ceil(to_char(sysdate,'MI')/30)*30/1440

begin
  sys.dbms_job.change(job => xxx,
                      what => 'yyy;',
                      next_date => sysdate,
                      interval => 'trunc(sysdate,''HH'')+8/1440+ceil(to_char(sysdate,''MI'')/30)*30/1440');
  commit;
end;
/