oracle表没被锁删不掉,oracle-锁定从父表删除而不是错误

我有Oracle数据库11g企业版11.2.0.1.0版.

我有父表t1和t2,并带有引用t1(col1)的外键.

我想知道的是为什么有锁？

请检查我做了什么…

第一场

SQL> create table t1(col1 char(1), primary key(col1));

Table created.

SQL> insert into t1 values('1');

1 row created.

SQL> insert into t1 values('2');

1 row created.

SQL> insert into t1 values('3');

1 row created.

SQL> insert into t1 values('4');

1 row created.

SQL> insert into t1 values('5');

1 row created.

SQL> commit;

Commit complete.

SQL> create table t2(col1 char(1), col2 char(2), foreign key(col1) references t1(col1));

Table created.

SQL> insert into t2 values('1','0');

1 row created.

SQL> commit;

Commit complete.

SQL> update t2 set col2='9'; --not committed yet!

1 row updated.

第二场

SQL> delete from t1; -- Lock happens here!!!

第一场

SQL> commit;

Commit complete.

第二场

delete from t1 -- The error occurs after I commit updating query in session 1.

*

ERROR at line 1:

ORA-02292: integrity constraint (KMS_USER.SYS_C0013643) violated - child record found

谁能解释我为什么会这样？