Hi , Mr. Thomasps ,
sorry that you totally misunderstood what I mean .

Surely trancate will reset HWM and deallocate all the space (without issuing alter table deallocate command)

But What I mean is after issue delete form table plus issue

alter table deallocate command (do you know the meaning of deallocate ? Please check oracle manual ) , why the hwm is down aroudn 20% ( not 0 % and not 100% , do you think it is strange ?)

Please think again and welcome your reply .

something looks simply but actually not simply :-)