1.1
create table Addressbook
(
regist_no integer not null,
name varchar(128) not null,
address varchar(256) not null,
tel_no char(10) null,
mail_address char(20),
primary key (regist_no)
)
1.2
alter table addressbook add postal_code char(8) not null
1.3
drop table addressbook
1.4
无法使用命令恢复,重新创建所需表