从11.1开始密码大小写敏感了，同时可以设置sec_case_sensitive_logon参数可以忽略大小写敏感。
通过朋友咨询的不设置sec_case_sensitive_logon参数让密码大小写不敏感的实验这篇文章疑惑,同时也感谢朋友让我学习到了新知识,我通过测试证明了如下结论：
1.password_versions的优先级大于sec_case_sensitive_logon
2.通过修改USER$.SPARE4为空实现了屏蔽ORACLE 11g密码大小写敏感

10g创建用户导出数据

SQL> create user ora10g identified by xifenfei;
User created.
SQL> grant connect to ora10g;
Grant succeeded.
C:\Documents and Settings\Administrator>expdp \"/ as sysdba \" DIRECTORY=exp_dp
DUMPFILE=chf.dmp schemas=ora10g
Export: Release 10.2.0.1.0 - Production on 星期三, 15 5月, 2013 22:59:45
Copyright (c) 2003, 2005, Oracle.  All rights reserved.
连接到: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
启动 "SYS"."SYS_EXPORT_SCHEMA_01":  "/******** AS SYSDBA" DIRECTORY=exp_dp DUMPF
ILE=chf.dmp schemas=ora10g
正在使用 BLOCKS 方法进行估计...
处理对象类型 SCHEMA_EXPORT/TABLE/TABLE_DATA
使用 BLOCKS 方法的总估计: 0 KB
处理对象类型 SCHEMA_EXPORT/USER
处理对象类型 SCHEMA_EXPORT/ROLE_GRANT
处理对象类型 SCHEMA_EXPORT/DEFAULT_ROLE
处理对象类型 SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
已成功加载/卸载了主表 "SYS"."SYS_EXPORT_SCHEMA_01"
******************************************************************************
SYS.SYS_EXPORT_SCHEMA_01 的转储文件集为:
  C:\CHF.DMP
作业 "SYS"."SYS_EXPORT_SCHEMA_01" 已于 23:00:19 成功完成

11g创建用户

SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
SQL> show parameter logon
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
sec_case_sensitive_logon             boolean     TRUE
SQL> create user ora11g identified by xifenfei;
User created.
SQL> grant connect to ora11g;
Grant succeeded.
SQL> conn ora11g/xifenfei
Connected.
SQL> conn ora11g/XIFENFEI
ERROR:
ORA-01017: invalid username/password; logon denied
Warning: You are no longer connected to ORACLE.

这里证明,在sec_case_sensitive_logon=true的情况下,数据库密码是大小写敏感

导入10g创建用户dmp文件

[oracle@localhost ~]$ impdp '"/ as sysdba"' directory=exp_dp dumpfile=CHF.DMP
Import: Release 11.2.0.3.0 - Production on Wed May 15 23:07:20 2013
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Master table "SYS"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYS"."SYS_IMPORT_FULL_01":  "/******** AS SYSDBA" directory=exp_dp dumpfile=CHF.DMP
Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Job "SYS"."SYS_IMPORT_FULL_01" successfully completed at 23:07:21

查询ora10g和ora11g用户区别

SQL> conn ora10g/xifenfei
Connected.
SQL> conn ora10g/XIFENFEI
Connected.
SQL> conn / as sysdba
Connected.
SQL>  select t.username,t.account_status,t.password_versions from dba_users t where t.username in ('ORA11G','ORA10G');
USERNAME                       ACCOUNT_STATUS                   PASSWORD
------------------------------ -------------------------------- --------
ORA11G                         OPEN                             10G 11G
ORA10G                         OPEN                             10G
SQL> select name,password,spare4 from SYS.USER$ t where name in ('ORA11G','ORA10G');
NAME                           PASSWORD                       SPARE4
------------------------------ ------------------------------ ----------------------------------------------------------------
ORA10G                         F3CF2F0CB35CB6CA
ORA11G                         559D84354181EB8E               S:BFE2625310D9382E9AEA6EE0AA2988E82C17B3EA23E3DAC23800490C2621

这里可以发现我们从低版本(10g)导入到11g中的用户登录是不区分大小写,而11g本身创建的用户是区分大小写,而他们的区别仅仅是在dba_users.password_versions中有不一样,跟踪到基表发现就是USER$.SPARE4列不一样(10g的该列为空).
猜想:password_versions的优先级大于sec_case_sensitive_logon这个参数

验证猜想
如果是password_versions的优先级大于sec_case_sensitive_logon那么，如果我修改了USER$.SPARE4,使得dba_users.password_versions变成和10g导入的库一样,是否就可以实现不区分密码大小写的问题,如果不缺乏证明：password_versions的优先级大于sec_case_sensitive_logon这个参数,反之失败.

SQL> update SYS.USER$ t set SPARE4='' where name='ORA11G';
1 row updated.
SQL> COMMIT;
Commit complete.
SQL> alter system flush shared_pool;
System altered.
SQL> conn ora11g/XIFENFEI
Connected.
SQL> conn ora11g/xifenfei
Connected.

由此得出两个结论:
1.password_versions的优先级大于sec_case_sensitive_logon
2.通过修改USER$.SPARE4为空实现了屏蔽ORACLE 11g密码大小写敏感