$ exp username/password file=expdat.dmp tables=tablename
这是一条经历了磨难的语句，然而最终也还是修成正果
最开始报错：
EXP-00008: ORACLE error 904 encountered
ORA-00904: “DBMS_JAVA”.”LONGNAME”: invalid identifier
Export terminated successfully with warnings.
重新运行了$ORACLE_HOME/rdbms/admin/catexp.sql，无效，错误依旧。
然后运行$ORACLE_HOME/javavm/install/initdbj.sql，重新创建dbms_java包，这个错误消失了。
再次运行exp，报错：
Export done in US7ASCII character set and UTF8 NCHAR character set
server uses UTF8 character set (possible charset conversion)
EXP-00008: ORACLE error 6552 encountered
ORA-06552: PL/SQL: Compilation unit analysis terminated
ORA-06553: PLS-553: character set name is not recognized
Export terminated successfully with warnings.
检查系统环境，发现在props$中字符集是UTF8，但是操作系统环境变量没有设置NLS_LANG，于是：
NLS_LANG=AMERICAN_AMERICA.UTF8;export NLS_LANG
再次运行exp，仍然报错：
Export done in UTF8 character set and UTF8 NCHAR character set
EXP-00008: ORACLE error 6552 encountered
ORA-06552: PL/SQL: Compilation unit analysis terminated
ORA-06553: PLS-553: character set name is not recognized
Export terminated successfully with warnings.
于是询问客户是否有做过字符集的修改，果然，在很久很久以前，他们手动update props$表修改了字符集（手动修改props$是oracle7的招数，在oracle8和oracle9中虽然也能修改，但是会留下修改不干净的隐患）
首先，确认字符集是否修改的不彻底。
SELECT DISTINCT (NLS_CHARSET_NAME(CHARSETID)) CHARACTERSET,
DECODE(TYPE#,
1,
DECODE(CHARSETFORM,
1,
'VARCHAR2',
2,
'NVARCHAR2',
'UNKOWN'),
9,
DECODE(CHARSETFORM,
1,
'VARCHAR',
2,
'NCHAR VARYING',
'UNKOWN'),
96,
DECODE(CHARSETFORM, 1, 'CHAR', 2, 'NCHAR', 'UNKOWN'),
112,
DECODE(CHARSETFORM, 1, 'CLOB', 2, 'NCLOB', 'UNKOWN')) TYPES_USED_IN
FROM SYS.COL$
WHERE CHARSETFORM IN (1, 2)
AND TYPE# IN (1, 9, 96, 112);
CHARACTERSET TYPES_USED_IN
-------------------- -------------
AL16UTF16 NCHAR
AL16UTF16 NCLOB
AL16UTF16 NVARCHAR2
UTF8 CHAR
UTF8 VARCHAR2
WE8ISO8859P1 CHAR
WE8ISO8859P1 CLOB
WE8ISO8859P1 VARCHAR2
8 rows selected.
确实在数据库的列属性中仍然存在着多个字符集的设定，这是导致exp失败的原因。下面解决这个问题。
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
ALTER SYSTEM SET AQ_TM_PROCESSES=0;
ALTER DATABASE OPEN;
COL VALUE NEW_VALUE CHARSET SELECT VALUE FROM NLS_DATABASE_PARAMETERS WHERE PARAMETER='NLS_CHARACTERSET';
COL VALUE NEW_VALUE NCHARSET SELECT VALUE FROM NLS_DATABASE_PARAMETERS WHERE PARAMETER='NLS_NCHAR_CHARACTERSET';
--INTERNAL_USE是没有写在文档中的参数，用以强制完成字符集一致化
ALTER DATABASE CHARACTER SET INTERNAL_USE &CHARSET;
ALTER DATABASE NATIONAL CHARACTER SET INTERNAL_USE &NCHARSET;
SHUTDOWN IMMEDIATE;
STARTUP;
-- 再次启动数据库一遍
SHUTDOWN IMMEDIATE;
STARTUP;
按照上面的步骤，一步一步来，一步不要少，完成以后，重新检索col$表。
CHARACTERSET TYPES_USED_IN
-------------------- -------------
UTF8 CHAR
UTF8 CLOB
UTF8 NCHAR
UTF8 NCLOB
UTF8 NVARCHAR2
UTF8 VARCHAR2
干净了，再次运行exp，大功告成。
Export terminated successfully without warnings.
http://www.dbform.com/html/2007/309.html EXP错误逐个击溃