这段时间在做数据迁移，需要从10g的ZHS16GBK字符集的数据库里面迁移数据到11g的UTF8字符的数据库，并且源数据库的NLS_LENGTH_SEMANTICS参数值为Byte，目标端的NLS_LENGTH_SEMANTICS参数值为CHAR。如果直接从源使用exp/expdp导出数据，然后使用imp/impdp导入数据到目标的话，可能会出现数据超长的情况，这时候就不好搞了，因此我就使用了中转的方式。即，把源数据导入到NLS_LENGTH_SEMANTICS参数值为CHAR的ZHS16GBK字符集的中转数据库中，然后再从中转数据库中导出数据并导入到目标数据库中。
：这样做是有条件的，源数据库中没有长度超过4000/3个中文字符的CHAR/VARCHAR2字段，原因看这里
继续这个问题，之所以这么做，是为了在数据部超长的情况得到CHAR/VARCHAR2类型字段以CHAR存储的数据。
根据Oracle的定义，NLS_LENGTH_SEMANTICS参数可以在三个层次生效：数据库级、实例级、会话级，并且生效的优先顺序为会话级>实例级>数据库级。
但是，我发现了一个问题：不管把NLS_LENGTH_SEMANTICS在那个级别设置为CHAR，在Oracle 中，新表都做为CHAR/VARCHAR2等数据类型的存储单位，而是，除非源数据就已经指定了CHAR。
请看如下实验过程，全过程均使用普通用户，因为NLS_LENGTH_SEMANTICS参数对sys用户无效：
先查看NLS_LENGTH_SEMANTICS参数，Database、Instance和Session都设置为CHAR
srcbdb@SYS> select * from nls_session_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS
srcbdb@SYS> select * from nls_instance_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS
srcbdb@SYS> select * from nls_database_parameters where PARAMETER='NLS_LENGTH_SEMANTICS';
PARAMETER VALUE
------------------------------ --------------------------------------------------
NLS_LENGTH_SEMANTICS
然后倒入数据
[oracle@instsvr1 dumpdp]$ impdp vip/vip directory=dumpdir dumpfile=vip.byte.dat logfile=$ORACLE_SID.vip.impdp.`date +'%Y%m%d%H%M%S'`.log
Import: Release 11.2.0.1.0 - Production on Wed Mar 7 16:21:03 2012
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
Master table "VIP"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "VIP"."SYS_IMPORT_FULL_01": vip/******** directory=dumpdir dumpfile=vip.byte.dat logfile=srcbdb.vip.impdp.20120307162103.log
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/DB_LINK
ORA-31685: Object type DB_LINK:"VIP"."DB_SRCBDATA" failed due to insufficient privileges. Failing sql is:
CREATE DATABASE LINK "DB_SRCBDATA" CONNECT TO "SRCBDATA" IDENTIFIED BY VALUES '053E86648883623A93807EAD3C7A2EA776FA8F916A941AFB2E' USING 'srcbfin'
Processing object type SCHEMA_EXPORT/SEQUENCE/SEQUENCE
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type SCHEMA_EXPORT/TABLE/COMMENT
Processing object type SCHEMA_EXPORT/FUNCTION/FUNCTION
Processing object type SCHEMA_EXPORT/PROCEDURE/PROCEDURE
Processing object type SCHEMA_EXPORT/FUNCTION/ALTER_FUNCTION
Processing object type SCHEMA_EXPORT/PROCEDURE/ALTER_PROCEDURE
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Job "VIP"."SYS_IMPORT_FULL_01" completed with 1 error(s) at 16:24:48
查看表结构
[oracle@instsvr1 dumpdp]$ sqlplus vip/vip
SQL*Plus: Release 11.2.0.1.0 Production on Wed Mar 7 14:56:04 2012
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options
srcbdb@VIP> select * from tab where rownum desc SNAPTBEXCHANGERATE
Name Null? Type
----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------
MONEY_TYPE create table lzb (col1 char(10),col2 varchar2(10));
Table created.
srcbdb@VIP> desc lzb
Name Null? Type
----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------
COL1