Oracle資料庫中外鍵的相關操作整理_oracle

racle使用外鍵來限制子表中參考的欄位值，要求子表中的資料必須在主表中存在。當主表的記錄發生變化時導致外鍵參考唯一約束值發生了變化時，Oracle指定了三種動作：預設值（類似於restrict）、delete cascade和delete set null。(
1.建立父表並初始化資料

SQL> create table t_parent (parent_id int primary key, name varchar2(10));Table created.SQL> insert into t_parent values (1,'record1');1 row created.SQL> insert into t_parent values (2,'record2');1 row created.SQL> insert into t_parent values (3,'record3');1 row created.SQL> commit;Commit complete.

2.建立三種類型的子表t_child1、t_child2和t_child3
(1)no action類別

SQL> create table t_child1 (child1_id int primary key, parent_id int);Table created.SQL> alter table t_child1 add constraint FK_t_child1 foreign key (parent_id) references t_parent (parent_id);Table altered.SQL> insert into t_child1 values (1,1);1 row created.SQL> commit;Commit complete.

(2)cascade類型

SQL> create table t_child2 (child2_id int primary key, parent_id int);Table created.SQL> alter table t_child2 add constraint FK_t_child2 foreign key (parent_id) references t_parent (parent_id) on delete cascade;Table altered.SQL> insert into t_child2 values (2,2);1 row created.SQL> commit;Commit complete.

(3)SET NULL類型

SQL> create table t_child3 (child2_id int primary key, parent_id int);Table created.SQL> alter table t_child3 add constraint FK_t_child3 foreign key (parent_id) references t_parent (parent_id) on delete set null;Table altered.SQL> insert into t_child3 values (3,3);1 row created.SQL> commit;Commit complete.

3.確認主表和子表中的資料

SQL> select * from T_PARENT;PARENT_ID NAME---------- ----------     1 record1     2 record2     3 record3SQL> select * from T_CHILD1;CHILD1_ID PARENT_ID---------- ----------     1     1SQL> select * from T_CHILD2; CHILD2_ID PARENT_ID---------- ----------     2     2SQL> select * from T_CHILD3; CHILD2_ID PARENT_ID---------- ----------     3     3

4.嘗試對具有預設類型外鍵參照的主表記錄進行刪除

SQL> delete from T_PARENT where parent_id = 1;delete from T_PARENT where parent_id = 1*ERROR at line 1:ORA-02292: integrity constraint (HBHE.FK_T_CHILD1) violated - child recordfoundSQL> select * from T_CHILD1; CHILD1_ID PARENT_ID---------- ----------     1     1

在此類型下，不允許刪除操作

5.嘗試對具有delete cascade類型外鍵參照的主表記錄進行刪除

SQL> delete from T_PARENT where parent_id = 2;1 row deleted.SQL> select * from T_CHILD2;no rows selected

串聯刪除成功

6.嘗試對具有delete set null類型外鍵參照的主表記錄進行刪除

SQL> delete from T_PARENT where parent_id = 3;1 row deleted.SQL> select * from T_CHILD3; CHILD2_ID PARENT_ID---------- ----------     3

  主表記錄可以完成刪除，子表中對應的內容被設定為NULL。