对于DBA来说，最常见一个例子是可以使用外部表来访问警告日志文件或其他跟踪文件.
以下一个例子用来说明外部表的用途。
[oracle@jumper oracle]$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.4.0 - Production on Sun Oct 15 21:42:28 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production
SQL> create or replace directory bdump
2 as '/opt/oracle/admin/eygle/bdump';
Directory created.
SQL> col DIRECTORY_PATH for a30
SQL> col owner for a10
SQL> select * from dba_directories;
OWNER DIRECTORY_NAME DIRECTORY_PATH
---------- ------------------------------ ------------------------------
SYS BDUMP /opt/oracle/admin/eygle/bdump
SQL> select * from alert_log where rownum < 51;
TEXT
-----------------------------------------------------------------------------------------
Mon Jun 26 12:00:24 2006
Starting ORACLE instance (normal)
Mon Jun 26 12:00:25 2006
WARNING: EINVAL creating segment of size 0x0000000008c00000
fix shm parameters in /etc/system or equivalent
LICENSE_MAX_SESSION = 0
LICENSE_SESSIONS_WARNING = 0
SCN scheme 2
Using log_archive_dest parameter default value
LICENSE_MAX_USERS = 0
SYS auditing is disabled
Starting up ORACLE RDBMS Version: 9.2.0.4.0.
System parameters with non-default values:
processes = 150
timed_statistics = TRUE
shared_pool_size = 104857600
large_pool_size = 0
java_pool_size = 0
control_files = /opt/oracle/oradata/eygle/control01.ctl
db_block_size = 8192
db_cache_size = 16777216
db_cache_advice = ON
compatible = 9.2.0.0.0
db_file_multiblock_read_count= 16
fast_start_mttr_target = 300
log_checkpoints_to_alert = TRUE
undo_management = AUTO
undo_tablespace = UNDOTBS1
undo_retention = 10800
remote_login_passwordfile= EXCLUSIVE
db_domain =
instance_name = eygle
job_queue_processes = 10
hash_join_enabled = TRUE
background_dump_dest = /opt/oracle/admin/eygle/bdump
user_dump_dest = /opt/oracle/admin/eygle/udump
core_dump_dest = /opt/oracle/admin/eygle/cdump
sort_area_size = 524288
db_name = eygle
open_cursors = 500
star_transformation_enabled= FALSE
query_rewrite_enabled = FALSE
pga_aggregate_target = 52428800
aq_tm_processes = 0
PMON started with pid=2
DBW0 started with pid=3
LGWR started with pid=4
CKPT started with pid=5
SMON started with pid=6
RECO started with pid=7
50 rows selected.
SQL>
如果我们需要查看数据库中曾经出现过的ORA-错误，那么可以执行如下查询:
SQL> select * from alert_log where text like 'ORA-%';
TEXT
-----------------------------------------------------------------------------------
ORA-1652: unable to extend temp segment by 128 in tablespace TEMP
