DEFERRABLE约束切换实验

EODA@PROD1> set echo on
EODA@PROD1> create table parent ( pk  int primary key );

Table created.

EODA@PROD1> create table child
2    ( fk  constraint child_fk_parent
3          references parent(pk)
4          deferrable       --设置为有可延迟的约束
5          initially immediate
6    )
7  /

Table created.

EODA@PROD1> insert into parent values ( 1 );

1 row created.

EODA@PROD1> insert into child values ( 1 );

1 row created.

EODA@PROD1> update parent set pk = 2;  --更新报错由于检查约束失败
update parent set pk = 2
*
ERROR at line 1:
ORA-02292: integrity constraint (EODA.CHILD_FK_PARENT) violated - child record found

EODA@PROD1> set constraint child_fk_parent deferred;  --设置为deferred约束模式

Constraint set.

EODA@PROD1> update parent set pk = 2;  --更新成功

1 row updated.

EODA@PROD1> set constraint child_fk_parent immediate;  --设置回immediate约束模式失败，因为当前状态违反约束
set constraint child_fk_parent immediate
*
ERROR at line 1:
ORA-02291: integrity constraint (EODA.CHILD_FK_PARENT) violated - parent key not found

EODA@PROD1> update child set fk = 2;  --修改子表

1 row updated.

EODA@PROD1> set constraint child_fk_parent immediate;  --设置成功

Constraint set.

EODA@PROD1> commit;

Commit complete.