mysql>insert intot_user(id,name,email)values(1,'xlj','932834897@qq.com');QueryOK,1rowaffected(0.00sec)mysql>insert intot_user(id,name,email)values(2,'jay','932834897@qq.com');ERROR1062(23000):Duplicate entry'932834897@qq.com'forkey'email' 六、主键约束(primary key)PK 表设计时一定要有...
(id), constraint stu_id_pk primary key (id), constraint stu_name_email_uni unique(email, name) ); create table class ( id number(4) primary key, name varchar2(20) not null ); 100、---修改表结构,添加字段--- alter table stu add(addr varchar2(29)); 101、---删除字段--- ...