alter table mytable add primary key(col[,df[,..]])
alter table mytable add constraint constraint_name primary key(col)
alter table mytable disable primary key
alter table mytable constraint 原主键名 to 新
alter table t1 add constraint fk_t1_t2 foreign key (cid) references t2(cid);
alter table emp add constraint fk_a foreign (empno) references dept(deptno) on delete cascade
alter table emp rename constraint fk1 to fk2
alter table tablea disabled constraint fk_1;
--关闭数据完整性交验
alter table purchase enable novalidate constraint fk
alter table tableA drop constraint my_pk 删除约束
alter table add constraint name unique(col1,col2);
alter table mytable add constraint cons_name check(col alter table mytable modify st default 'AC';\ alter table mytable modify(col1 not null)