参考自：
11g R1 New Feature : Case Sensitive Passwords and Strong User Authentication (文档 ID 429465.1)
The view DBA_USERS has new column PASSWORD_VERSIONS rendered as follows:
decode(length(u.password),16,‘10G ‘,NULL)||NVL2(u.spare4, ‘11G ‘ ,NULL)
for example:
SQL> select USERNAME, PASSWORD_VERSIONS from dba_users;
USERNAME PASSWORD
------------------------------ --------
...
SCOTT 10G 11G
In this case it means both old and new-style hash values ar available for user SCOTT, the new hash value is stored in the USER$.SPARE4 column, as long as this remains NULL it means the password has not been changed since the migration and the user will
have the old case insensitive password. If you want to enforce case sensitivity for users changing their passwords using a profile with a password_verify_function, check Note 1307555.1 for how to do this.
在reference中，PASSWORD_VERSIONS 列的解释如下：
Database version in which the password was created or changed
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