[Oracle]comment 주기

table or column에 comment 주기
        comment on table table_name is 'description';
        comment on column table_name.column_name is 'description';
        comment of up to 2000 bytes about a column, table, view, snapshot
        관련view : all(user)_col_comments, all(user)_tab_comments
        (column comments -> _col_ , table comments -> _tab_ )
    - object 이름 바꾸기 : rename old_name to new_name;