對於資料泵EXPDP/IMPDP而言，功能比普通EXP/IMP功能要強的多，因此也可以實現一些普通匯出匯入工具很難完成的工作。

比如今天碰到的這個問題，要匯出一些表，但是其中個別表只匯出結構而不匯出資料。

SQL> conn test/test
Connected.
SQL> set pages 100 lines 120
SQL> select count(*) from t;

COUNT(*)
----------
23

SQL> select count(*) from tt;

COUNT(*)
----------
72

SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
[oracle@yans1 ~]$ expdp test/test directory=d_output dumpfile=t_tt1.dp tables=(t,tt)

Export: Release 10.2.0.3.0 - 64bit Production on 星期二, 25 8月, 2009 16:04:58

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
Starting "TEST"."SYS_EXPORT_TABLE_01": test/******** directory=d_output dumpfile=t_tt1.dp tables=(t,tt)
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 256 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "TEST"."T" 5.953 KB 23 rows
. . exported "TEST"."TT" 6.421 KB 72 rows
Master table "TEST"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for TEST.SYS_EXPORT_TABLE_01 is:
/home/oracle/t_tt1.dp
Job "TEST"."SYS_EXPORT_TABLE_01" successfully completed at 16:05:02

用T和TT表作為例子，分別代表需要匯出結構的表和同時包含結構和資料的表。

這個需求對於普通的EXP/IMP來說，只能透過兩次匯出操作來完成，一次匯出包含資料的表，另一個透過執行ROWS=N匯出僅需要結構的表。

對於EXPDP來說，同樣可以使用類似的方法，引數CONTENT控制匯出的結構、資料還是全部：

[oracle@yans1 ~]$ expdp test/test directory=d_output dumpfile=t_tt2.dp tables=(t,tt) content=metadata_only

Export: Release 10.2.0.3.0 - 64bit Production on 星期二, 25 8月, 2009 16:32:59

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
Starting "TEST"."SYS_EXPORT_TABLE_01": test/******** directory=d_output dumpfile=t_tt2.dp tables=(t,tt) content=metadata_only
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Master table "TEST"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for TEST.SYS_EXPORT_TABLE_01 is:
/home/oracle/t_tt2.dp
Job "TEST"."SYS_EXPORT_TABLE_01" successfully completed at 16:33:02

但是這種方法控制的是整體，現在需要對其中的個別物件只匯出表結構。最好想到的方法是透過QUERY來控制：

[oracle@yans1 ~]$ expdp test/test directory=d_output dumpfile=t_tt3.dp tables=(t,tt) query='t:"where 1=2"'

Export: Release 10.2.0.3.0 - 64bit Production on 星期二, 25 8月, 2009 16:51:37

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
Starting "TEST"."SYS_EXPORT_TABLE_01": test/******** directory=d_output dumpfile=t_tt3.dp tables=(t,tt) query=t:"where 1=2"
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 256 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "TEST"."T" 5.507 KB 0 rows
. . exported "TEST"."TT" 6.421 KB 72 rows
Master table "TEST"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for TEST.SYS_EXPORT_TABLE_01 is:
/home/oracle/t_tt.dp
Job "TEST"."SYS_EXPORT_TABLE_01" successfully completed at 16:51:41

透過對T表新增一個恆為FALSE的查詢條件，使得T表匯出的時候獲取0條記錄，從而達到只導T的結構的目的。

但是這種方法對於資料量比較大的表效率會比較低，因為Oracle會進行匯出的操作，只是在處理的時候將記錄過濾掉，除了沒有將資料寫到匯出檔案，其他所有的操作都進行了，因此效率很低。

而實際上，資料泵還有更好的辦法來解決這個問題：使用EXCLUDE引數。

[oracle@yans1 ~]$ expdp test/test directory=d_output dumpfile=t_tt4.dp tables=(t,tt) exclude=table/table_data:\"=\'T\'\"

Export: Release 10.2.0.3.0 - 64bit Production on 星期二, 25 8月, 2009 16:59:39

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
Starting "TEST"."SYS_EXPORT_TABLE_01": test/******** directory=d_output dumpfile=t_tt4.dp tables=(t,tt) exclude=table/table_data:"='T'"
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 128 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "TEST"."TT" 6.421 KB 72 rows
Master table "TEST"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for TEST.SYS_EXPORT_TABLE_01 is:
/home/oracle/t_tt4.dp
Job "TEST"."SYS_EXPORT_TABLE_01" successfully completed at 16:59:43

這裡看不到T表的資訊，下面檢查一下匯出是否生效：

[oracle@yans1 ~]$ sqlplus test/test

SQL*Plus: Release 10.2.0.3.0 - Production on 星期二 8月 25 17:00:27 2009

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> desc t
Name                                      Null?    Type
----------------------------------------- -------- ----------------------------
ID                                                 NUMBER
NAME                                      NOT NULL VARCHAR2(30)
TYPE                                               VARCHAR2(7)

SQL> drop table t;

Table dropped.

SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
[oracle@yans1 ~]$ impdp test/test directory=d_output dumpfile=t_tt4.dp tables=t

Import: Release 10.2.0.3.0 - 64bit Production on 星期二, 25 8月, 2009 17:00:41

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
Master table "TEST"."SYS_IMPORT_TABLE_01" successfully loaded/unloaded
Starting "TEST"."SYS_IMPORT_TABLE_01": test/******** directory=d_output dumpfile=t_tt4.dp tables=t
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Job "TEST"."SYS_IMPORT_TABLE_01" successfully completed at 17:00:43

[oracle@yans1 ~]$ sqlplus test/test

SQL*Plus: Release 10.2.0.3.0 - Production on 星期二 8月 25 17:00:47 2009

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> desc t
Name                                      Null?    Type
----------------------------------------- -------- ----------------------------
ID                                                 NUMBER
NAME                                      NOT NULL VARCHAR2(30)
TYPE                                               VARCHAR2(7)

SQL> select * from t;

no rows selected

很顯然，利用EXCLUDE的方式使得資料泵匯出的時候去掉了T表的資料。

資料泵避免個別表資料的匯出

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