如何让SQLPLUS实现带日期的时间戳

from http://www.itpub.net/thread-1876506-4-1.html

SQL> define
DEFINE _DATE           = "20-7月 -14" (CHAR)
DEFINE _CONNECT_IDENTIFIER = "ORCL" (CHAR)
DEFINE _USER           = "SYSTEM" (CHAR)
DEFINE _PRIVILEGE      = "" (CHAR)
DEFINE _SQLPLUS_RELEASE = "1102000100" (CHAR)
DEFINE _EDITOR         = "Notepad" (CHAR)
DEFINE _O_VERSION      = "Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options" (CHAR)
DEFINE _O_RELEASE      = "1102000100" (CHAR)
SQL> set sqlprompt _DATE>

20-7月 -14>alter session set nls_date_format='YYYY-MM-DD HH:MI:SS';

会话已更改。

2014-07-20 12:54:33>