莫晓毅.txt

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1.
create table commodity (id int, cname varchar2(20),price int,cuzun int,zid int);
create table zhonglei  (zid int, zname varchar2(10),cname varchar2(20));
alter table commodity add constraint pk_com primary key(id);
alter table commodity modify price not null;
alter table commodity add constraint check_cz check (cuzun>0 or cuzun=0);
alter table commodity add constraint fg_com  foreign key(zid) references zhonglei(zid);
alter table zhonglei add constraint pk_zl primary key(zid);
alter table zhonglei add unique (cname);
alter table commodity add constraint fg_cn foreign key (cname) references zhonglei(cname);

2.
alter table commodity add (dazhe number);
alter table commodity modify (price number);
alter table commodity drop (dazhe);