aw *_*rud 17 sql oracle referential-integrity hierarchical-data
我有一个有3列的表:
ID, PARENT_ID, NAME
PARENT_IDID在同一个表中具有外键关系.该表正在为层次结构建模.
有时ID记录会改变.我希望能够更新记录ID,然后更新依赖记录' PARENT_ID以指向新记录ID.
问题是,当我尝试更新ID记录时,它会破坏完整性并立即失败.
我意识到我可以使用new插入一个新记录ID,然后更新子项,然后删除旧记录,但是我们有很多触发器,如果我这样做会搞砸.
有没有办法暂时更新父级,承诺更新子级(显然它会在提交时失败)而不会短暂禁用外键？
Chi*_*Chi 19
你想要的是一个' 可延迟的约束 '.
您可以在两种类型的可延迟约束之间进行选择,"初始立即"和"初始延迟"以驱动默认行为 - 数据库是否应该默认在每个语句之后检查约束,或者它是否应该默认只检查最后的约束交易.
Sha*_*nce 10
回答比Chi慢,但觉得包含代码示例会很好,所以答案可以在SO上找到.
正如Chi回答的那样,可延迟的约束使这成为可能.
SQL> drop table t;
Table dropped.
SQL> create table T (ID number
2 , parent_ID number null
3 , name varchar2(40) not null
4 , constraint T_PK primary key (ID)
5 , constraint T_HIREARCHY_FK foreign key (parent_ID)
6 references T(ID) deferrable initially immediate);
Table created.
SQL> insert into T values (1, null, 'Big Boss');
1 row created.
SQL> insert into T values (2, 1, 'Worker Bee');
1 row created.
SQL> commit;
Commit complete.
SQL> -- Since initially immediate, the following statement will fail:
SQL> update T
2 set ID = 1000
3 where ID = 1;
update T
*
ERROR at line 1:
ORA-02292: integrity constraint (S.T_HIREARCHY_FK) violated - child record found
SQL> set constraints all deferred;
Constraint set.
SQL> update T
2 set ID = 1000
3 where ID = 1;
1 row updated.
SQL> update T
2 set parent_ID = 1000
3 where parent_ID = 1;
1 row updated.
SQL> commit;
Commit complete.
SQL> select * from T;
ID PARENT_ID NAME
---------- ---------- ----------------------------------------
1000 Big Boss
2 1000 Worker Bee
SQL> -- set constraints all deferred during that transaction
SQL> -- and the transaction has commited, the next
SQL> -- statement will fail
SQL> update T
2 set ID = 1
3 where ID = 1000;
update T
*
ERROR at line 1:
ORA-02292: integrity constraint S.T_HIREARCHY_FK) violated - child record found
我相信,但找不到参考,延迟是在约束创建时定义的,不能在以后修改.默认值是不可延迟的.要更改为可延迟约束,您需要执行一次删除并添加约束.(正确安排,控制等)
SQL> drop table t;
Table dropped.
SQL> create table T (ID number
2 , parent_ID number null
3 , name varchar2(40) not null
4 , constraint T_PK primary key (ID)
5 , constraint T_HIREARCHY_FK foreign key (parent_ID)
6 references T(ID));
Table created.
SQL> alter table T drop constraint T_HIREARCHY_FK;
Table altered.
SQL> alter table T add constraint T_HIREARCHY_FK foreign key (parent_ID)
2 references T(ID) deferrable initially deferred;
Table altered.
这种情况的常见建议是采用可延迟约束.但是,我认为这些情况几乎总是应用程序逻辑或数据模型的失败.例如,如果我们将它作为两个语句执行,那么在同一个事务中插入子记录和父记录可能会有问题:
我的测试数据:
SQL> select * from t23 order by id, parent_id
2 /
ID PARENT_ID NAME
---------- ---------- ------------------------------
110 parent 1
111 parent 2
210 110 child 0
220 111 child 1
221 111 child 2
222 111 child 3
6 rows selected.
SQL>
做错的方法:
SQL> insert into t23 (id, parent_id, name) values (444, 333, 'new child')
2 /
insert into t23 (id, parent_id, name) values (444, 333, 'new child')
*
ERROR at line 1:
ORA-02291: integrity constraint (APC.T23_T23_FK) violated - parent key not
found
SQL> insert into t23 (id, parent_id, name) values (333, null, 'new parent')
2 /
1 row created.
SQL>
但是,Oracle支持多表INSERT synatx,它允许我们在同一语句中插入父记录和子记录,从而避免了对可延迟约束的需要:
SQL> rollback
2 /
Rollback complete.
SQL> insert all
2 into t23 (id, parent_id, name)
3 values (child_id, parent_id, child_name)
4 into t23 (id, name)
5 values (parent_id, parent_name)
6 select 333 as parent_id
7 , 'new parent' as parent_name
8 , 444 as child_id
9 , 'new child' as child_name
10 from dual
11 /
2 rows created.
SQL>
您所处的情况类似:您希望更新父记录的主键但由于子记录的存在而无法更新:并且您无法更新子记录,因为没有父键.22条军规:
SQL> update t23
2 set id = 555
3 where id = 111
4 /
update t23
*
ERROR at line 1:
ORA-02292: integrity constraint (APC.T23_T23_FK) violated - child record found
SQL> update t23
2 set parent_id = 555
3 where parent_id = 111
4 /
update t23
*
ERROR at line 1:
ORA-02291: integrity constraint (APC.T23_T23_FK) violated - parent key not
found
SQL>
再次解决方案是在单个语句中执行:
SQL> update t23
2 set id = decode(id, 111, 555, id)
3 , parent_id = decode(parent_id, 111, 555, parent_id)
4 where id = 111
5 or parent_id = 111
6 /
4 rows updated.
SQL> select * from t23 order by id, parent_id
2 /
ID PARENT_ID NAME
---------- ---------- ------------------------------
110 parent 1
210 110 child 0
220 555 child 1
221 555 child 2
222 555 child 3
333 new parent
444 333 new child
555 parent 2
8 rows selected.
SQL>
UPDATE语句中的语法有点笨拙,但通常是kludges.关键是我们不应经常更新主键列.实际上,由于不变性是"主要关键"的特征之一,我们根本不应该真正更新它们.需要这样做是数据模型的失败.避免此类失败的一种方法是使用合成(代理)主键,并使用唯一约束简单地强制使用自然(也称为业务)键的唯一性.
那么为什么Oracle会提供可延迟的约束呢？当我们进行数据迁移或批量数据上传时,它们非常有用.它们允许我们清理数据库中的数据而无需登台表.我们真的不应该将它们用于常规应用程序任务.