create table periodical( autoid int not null,constraint a primary key(autoid));创建有主键的表
alter table periodical drop constraint a;删除主键
alter table periodical add constraint a primary key(autoid);增加主键
create table periodical( autoid int not null,constraint a primary key(autoid));创建有主键的表
alter table periodical drop constraint a;删除主键
alter table periodical add constraint a primary key(autoid);增加主键