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