1.可延迟约束
SELECT * FROM user_constraints 查询所有约束
alter table child add constraint fk_child foreign key (parent_name)
references parent (parent_name) deferrable ;
取消延迟:
set constraint fk_child immediate ;
2.检查约束
alter table temp add constraint ck_temp_age check ((age>0) and (age <= 125))
3.自引用约束
alter table professors add constraint fk_professors_prof_name foreign key (dept_head)
references professors (prof_name);--当然prof_name需为primary key;
4.禁用/激活约束(禁用/激活约束会引起删除和重建索引的操作)
alter table employees disable/enable unique email
alter table employees disable/enable constraint emp_ename_pk
alter tabel employees modify constraint emp_pk disable/enable
alter tabel employees modify constraint emp_ename_phone_uk disable/enable
ALTER TABLE employees DROP CONSTRAINT emp_deptno_fk;删除约束
5.级联删除
alter table students add constraint fk_students_state foreign key (state) references state_lookup(state) on delete cascade ;
6.多列属性约束
alter table students add constraint uk_students_lic unique (state,license) ;
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