触发器学习

触发器：

create or replace trigger MyTrig1
  before update on cm_customer  
  for each row
declare
  -- local variables here
begin
  RAISE_APPLICATION_ERROR(-20500,
                          'You may insert' ||
                          ' into EMPLOYEES table only during ' ||
                          ' business hours.');
  dbms_output.put_line('update...');
end MyTrig1;