第三步报错ORA-00054和LOCK table无关，
而是和和第二步insert没有提交有关。
insert已经其他DML语句执行的时候会给相关对象加个TM锁，以防止该对象再被操作的时候(DML--数据操控语言)发生结构改变，即使DDL语句。
SQL> create table t1 (c1 char(2));
Table created.
SQL> select userenv('SID') from dual;
USERENV('SID')
--------------
1596
SQL> insert into t1 values('1');
1 row created.
SQL> select type,id1,id2 from v$lock where sid='1596';
TY ID1 ID2
-- ---------- ----------
AE 100 0
TM 593805 0
TX 3670041 37004435
3 rows selected.
SQL> select object_name from dba_objects where object_id=593805;
OBJECT_NAME
------------------------------
T1
1 row selected.
这时候在另外一个会话里
SQL> truncate table t1;
truncate table t1
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired
SQL> lock table t1 in exclusive mode nowait;
lock table t1 in exclusive mode nowait
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired
SQL> lock table t1 in exclusive mode; --一直等待，
lock table t1 in exclusive mode
*
ERROR at line 1:
ORA-01013: user requested cancel of current operation --用户手动终止
SQL> alter table t1 add (c2 number); --一直等待
alter table t1 add (c2 number)
*
ERROR at line 1:
ORA-01013: user requested cancel of current operation --用户手动终止