Oracle USERENV和sys_context

1.USEREVN()
返回当前用户环境的信息,opt可以是:
ENTRYID,SESSIONID,TERMINAL,ISDBA,LABLE,LANGUAGE,CLIENT_INFO,LANG,VSIZE
1.ISDBA   查看当前用户是否是DBA如果是则返回true
SQL> select userenv('isdba') from dual;
USEREN
------
FALSE
2.SESSION 返回会话标志
SQL> select userenv('sessionid') from dual;
USERENV('SESSIONID')
--------------------
                  152
4.ENTRYID 返回会话人口标志
SQL> select userenv('entryid') from dual;
USERENV('ENTRYID')
------------------
                  0
5.INSTANCE 返回当前INSTANCE的标志
SQL> select userenv('instance') from dual;
USERENV('INSTANCE')
-------------------
                   1
6.LANGUAGE 返回当前环境变量
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
----------------------------------------------------
SIMPLIFIED CHINESE_CHINA.ZHS16GBK
7.LANG 返回当前环境的语言的缩写
SQL> select userenv('lang') from dual;
USERENV('LANG')
----------------------------------------------------
ZHS
8.TERMINAL 返回用户的终端或机器的标志
SQL> select userenv('terminal') from dual;
USERENV('TERMINA
----------------
GAO
9.VSIZE(X) 返回X的大小(字节)数
SQL> select vsize(user),user from dual;
VSIZE(USER) USER
----------- ------------------------------
           6 SYSTEM
2.sys_context
　　select
　　SYS_CONTEXT('USERENV','TERMINAL') terminal,
　　SYS_CONTEXT('USERENV','LANGUAGE') language,
　　SYS_CONTEXT('USERENV','SESSIONID') sessionid,
　　SYS_CONTEXT('USERENV','INSTANCE') instance,
　　SYS_CONTEXT('USERENV','ENTRYID') entryid,
　　SYS_CONTEXT('USERENV','ISDBA') isdba,
　　SYS_CONTEXT('USERENV','NLS_TERRITORY') nls_territory,
　　SYS_CONTEXT('U