[轉自：http://space.itpub.net/519536/viewspace-631445]
當使用IMPDP完成數據庫導入時，如遇到表已存在時，Oracle提供給我們如下四種處理方式：
a.忽略（SKIP，默認行為）；
b.在原有數據基礎上繼續增加（APPEND）；
c.先DROP表，然后創建表，最后完成數據插入（REPLACE）；
d.先TRUNCATE，再完成數據插入（TRUNCATE）。
真實感受一下這幾種方式的效果，供參考。
1.IMPDP在線幫助中關於TABLE_EXISTS_ACTION參數的描述
TABLE_EXISTS_ACTION Action to take if imported object already exists.
Valid keywords: (SKIP), APPEND, REPLACE and TRUNCATE.
2.Oracle官方文檔中的描述
http://download.oracle.com/docs/cd/B19306_01/server.102/b14215/dp_import.htm#sthref365
Oracle官方文檔是根本，需研讀。
3.使用EXPDP生成一份dump文件
sec@secDB /expdp$ expdp sec/sec directory=expdp_dir dumpfile=`date +"%Y%m%d%H%M%S"`_sec.dmp logfile=`date +"%Y%m%d%H%M%S"`_sec.log
Export: Release 10.2.0.3.0 - 64bit Production on Thursday, 01 April, 2010 10:29:17
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Starting "SEC"."SYS_EXPORT_SCHEMA_01": sec/******** directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec.log
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 3 MB
Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
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
. . exported "SEC"."T" 2.259 MB 24360 rows
Master table "SEC"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SEC.SYS_EXPORT_SCHEMA_01 is:
/expdp/20100401102917_sec.dmp
Job "SEC"."SYS_EXPORT_SCHEMA_01" successfully completed at 10:29:20
4.分別使用四中方式真實的感知一下具體效果
用到的IMPDP語句統一匯總在這里，方便參考。
impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=SKIP
impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=APPEND
impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=REPLACE
impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=TRUNCATE
1）默認行為SKIP
sec@ora10g> select count(*) from t;
COUNT(*)
----------
24360
sec@secDB /expdp$ impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log
Import: Release 10.2.0.3.0 - 64bit Production on Thursday, 01 April, 2010 10:50:41
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Master table "SYSTEM"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_FULL_01": system/******** directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log
Processing object type SCHEMA_EXPORT/USER
ORA-31684: Object type USER:"SEC" already exists
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
ORA-39151: Table "SEC"."T" exists. All dependent metadata and data will be skipped due to table_exists_action of skip
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
Job "SYSTEM"."SYS_IMPORT_FULL_01" completed with 2 error(s) at 10:50:42
上面的行為與下面一條顯示的指定“SKIP”效果是一樣的，不贅述。
sec@secDB /expdp$ impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=SKIP
2）APPEND方式
sec@secDB /expdp$ impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=APPEND
Import: Release 10.2.0.3.0 - 64bit Production on Thursday, 01 April, 2010 10:51:32
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Master table "SYSTEM"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_FULL_01": system/******** directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=APPEND
Processing object type SCHEMA_EXPORT/USER
ORA-31684: Object type USER:"SEC" already exists
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
ORA-39152: Table "SEC"."T" exists. Data will be appended to existing table but all dependent metadata will be skipped due to table_exists_action of append
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
. . imported "SEC"."T" 2.259 MB 24360 rows
Job "SYSTEM"."SYS_IMPORT_FULL_01" completed with 2 error(s) at 10:51:33
此時表T的記錄數翻倍。
sec@ora10g> select count(*) from t;
COUNT(*)
----------
48720
3）REPLACE方式
sec@secDB /expdp$ impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=REPLACE
Import: Release 10.2.0.3.0 - 64bit Production on Thursday, 01 April, 2010 10:54:28
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Master table "SYSTEM"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_FULL_01": system/******** directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=REPLACE
Processing object type SCHEMA_EXPORT/USER
ORA-31684: Object type USER:"SEC" already exists
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
. . imported "SEC"."T" 2.259 MB 24360 rows
Job "SYSTEM"."SYS_IMPORT_FULL_01" completed with 1 error(s) at 10:54:29
sec@ora10g> select count(*) from t;
COUNT(*)
----------
24360
4）TRUNCATE方式
sec@secDB /expdp$ impdp system/sys directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=TRUNCATE
Import: Release 10.2.0.3.0 - 64bit Production on Thursday, 01 April, 2010 10:54:55
Copyright (c) 2003, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Master table "SYSTEM"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_FULL_01": system/******** directory=expdp_dir dumpfile=20100401102917_sec.dmp logfile=20100401102917_sec_impdp.log TABLE_EXISTS_ACTION=TRUNCATE
Processing object type SCHEMA_EXPORT/USER
ORA-31684: Object type USER:"SEC" already exists
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
ORA-39153: Table "SEC"."T" exists and has been truncated. Data will be loaded but all dependent metadata will be skipped due to table_exists_action of truncate
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
. . imported "SEC"."T" 2.259 MB 24360 rows
Job "SYSTEM"."SYS_IMPORT_FULL_01" completed with 2 error(s) at 10:54:56
sec@ora10g> select count(*) from t;
COUNT(*)
----------
24360
5.小結
IMPDP的TABLE_EXISTS_ACTION參數相比IMP工具是一個進步，我們的控制手段得到加強，莫要固步自封。