错误示范：
SQL> alter system set nls_date_format='yyyy-mm-dd 24hh:mi:ss' scope=spfile;
System altered.
我更改了数据库的日期格式后，重启后，数据库打开不了了。
ORA-01821: date format not recognized，有没有人知道怎么改回去。
大意 hh24 写成了24hh
解决步骤：
1.可能需要重配netca，启动监听到实例。
2.startup pfile=/u01/app/oracle/admin/orcl/pfile/init.ora.6272016162851;
ORACLE instance started.
Total System Global Area 672256000 bytes
Fixed Size 2216384 bytes
Variable Size 402656832 bytes
Database Buffers 264241152 bytes
Redo Buffers 3141632 bytes
Database mounted.
Database opened.
3.SQL> create spfile from pfile='/u01/app/oracle/admin/orcl/pfile/init.ora.6272016162851'; （重建spfile）
File created.
4.SQL> shutdown normal;
Database closed.
Database dismounted.
ORACLE instance shut down.
5.SQL> startup;
ORACLE instance started.
Total System Global Area 672256000 bytes
Fixed Size 2216384 bytes
Variable Size 402656832 bytes
Database Buffers 264241152 bytes
Redo Buffers 3141632 bytes
Database mounted.
Database opened.