我们一般使用dbms_metadata.get_ddl获取对象的ddl的时候，有时会获取一些其他额外的信息，例如当你想获取表的创建语句的时候，你会得到表的约束信息，这个信息可能是你不想要的，那么就可以用SESSION_TRANSFORM对它进行过滤。
看下面的示例，创建一个有主键和外键的表，获取他的ddl语句：
SQL> CREATE TABLE tb1 (id int primary key);
Table created.
SQL> create table tb2 (id int primary key references tb1(id));
Table created.
SQL> insert into tb1 values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> insert into tb2 values(1);
1 row created.
SQL> commit;
SQL> select dbms_metadata.get_ddl('TABLE','TB2','TEST') from dual;
DBMS_METADATA.GET_DDL('TABLE','TB2','TEST')
--------------------------------------------------------------------------------
CREATE TABLE "TEST"."TB2"
( "ID" NUMBER(*,0),
PRIMARY KEY ("ID")
USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DE
FAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "USERS" ENABLE,
FOREIGN KEY ("ID")
REFERENCES "TEST"."TB1" ("ID") ENABLE
) SEGMENT CREATION IMMEDIATE
PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DE
FAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "USERS"
不单单是获取到了创建的基本字段的语句，还有主键，约束，外键，存储参数，表空间等，如果这些你不需要，都是可以进行过滤的，例如我过滤掉主键、外键、存储信息
使用如下语句：
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,‘REF_CONSTRAINTS‘,false);
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,‘CONSTRAINTS‘,false);
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,‘STORAGE‘,false);
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,'REF_CONSTRAINTS',false);
PL/SQL procedure successfully completed.
exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,'CONSTRAINTS',false);
PL/SQL procedure successfully completed.
SQL> exec DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,'STORAGE',false);
PL/SQL procedure successfully completed.
SQL>
SQL> select dbms_metadata.get_ddl('TABLE','TB2','TEST') from dual;
DBMS_METADATA.GET_DDL('TABLE','TB2','TEST')
--------------------------------------------------------------------------------
CREATE TABLE "TEST"."TB2"
( "ID" NUMBER(*,0)
) SEGMENT CREATION IMMEDIATE
PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
TABLESPACE "USERS"
还可以对其他的一些信息做过滤，表格如下：Table 87-22 SET_TRANSFORM_PARAM: Transform Parameters for the DDLTransform
|
Object Type |
Name |
Datatype |
Meaning |
|
All objects |
PRETTY |
BOOLEAN |
If TRUE, format the output with indentation and line feeds. Defaults toTRUE. |
|
All objects |
SQLTERMINATOR |
BOOLEAN |
If TRUE, append a SQL terminator (; or /) to each DDL statement. Defaults to FALSE. |
|
TABLE |
SEGMENT_ATTRIBUTES |
BOOLEAN |
If TRUE, include segment attributes clauses in the DDL. If FALSE, omit them. Defaults to TRUE. |
|
TABLE |
STORAGE |
BOOLEAN |
If TRUE, include storage clauses in the DDL. If FALSE, omit them. Defaults to TRUE. (Ignored if SEGMENT_ATTRIBUTES is FALSE.) |
|
TABLE |
TABLESPACE |
BOOLEAN |
If TRUE, include tablespace clauses in the DDL. If FALSE, omit them. (Ignored if SEGMENT_ATTRIBUTES is FALSE.) Defaults to TRUE. |
|
TABLE |
CONSTRAINTS |
BOOLEAN |
If TRUE, include all non-referential table constraints in the DDL. If FALSE, omit them. Defaults to TRUE. |
|
TABLE |
REF_CONSTRAINTS |
BOOLEAN |
If TRUE, include all referential constraints (foreign keys) in the DDL. IfFALSE, omit them. Defaults to TRUE. |
|
TABLE |
CONSTRAINTS_AS_ALTER |
BOOLEAN |
If TRUE, include table constraints as separate ALTER TABLE (and, if necessary, CREATE INDEX) statements. If FALSE, specify table constraints as part of the CREATE TABLE statement. Defaults to FALSE. Requires thatCONSTRAINTS be TRUE. |
|
TABLE |
OID |
BOOLEAN |
If TRUE, include the OID clause for object tables in the DDL. If FALSE, omit it. Defaults to FALSE. |
|
TABLE |
SIZE_BYTE_KEYWORD |
BOOLEAN |
If TRUE, include the BYTE keyword as part of the size specification ofCHAR and VARCHAR2 columns that use byte semantics. If FALSE, omit the keyword. Defaults to FALSE. |
|
TABLE, INDEX |
PARTITIONING |
BOOLEAN |
If TRUE, include partitioning clauses in the DDL. If FALSE, omit them. Defaults to TRUE. |
|
INDEX, CONSTRAINT,ROLLBACK_SEGMENT,CLUSTER, TABLESPACE |
SEGMENT_ATTRIBUTES |
BOOLEAN |
If TRUE, include segment attributes clauses (physical attributes, storage attributes, tablespace, logging) in the DDL. If FALSE, omit them. Defaults to TRUE. |
|
INDEX, CONSTRAINT,ROLLBACK_SEGMENT, CLUSTER |
STORAGE |
BOOLEAN |
If TRUE, include storage clauses in the DDL. If FALSE, omit them. (Ignored if SEGMENT_ATTRIBUTES is FALSE.) Defaults to TRUE. |
|
INDEX, CONSTRAINT,ROLLBACK_SEGMENT, CLUSTER |
TABLESPACE |
BOOLEAN |
If TRUE, include tablespace clauses in the DDL. If FALSE, omit them. (Ignored if SEGMENT_ATTRIBUTES is FALSE.) Defaults to TRUE. |
|
TYPE |
SPECIFICATION |
BOOLEAN |
If TRUE, include the type specification in the DDL. If FALSE, omit it. Defaults to TRUE. |
|
TYPE |
BODY |
BOOLEAN |
If TRUE, include the type body in the DDL. If FALSE, omit it. Defaults toTRUE. |
|
TYPE |
OID |
BOOLEAN |
If TRUE, include the OID clause in the DDL. If FALSE, omit it. Defaults toFALSE. |
|
PACKAGE |
SPECIFICATION |
BOOLEAN |
If TRUE, include the package specification in the DDL. If FALSE, omit it. Defaults to TRUE. |
|
PACKAGE |
BODY |
BOOLEAN |
If TRUE, include the package body in the DDL. If FALSE, omit it. Defaults to TRUE. |
|
VIEW |
FORCE |
BOOLEAN |
If TRUE, use the FORCE keyword in the CREATE VIEW statement. If FALSE, do not use the FORCE keyword in the CREATE VIEW statement. Defaults toTRUE. |
|
OUTLINE |
INSERT |
BOOLEAN |
If TRUE, include the INSERT statements into the OL$ dictionary tables that will create the outline and its hints. If FALSE, omit a CREATE OUTLINEstatement. Defaults to FALSE. Note: This object type is being deprecated. |
|
All objects |
DEFAULT |
BOOLEAN |
Calling SET_TRANSFORM_PARAM with this parameter set to TRUE has the effect of resetting all parameters for the transform to their default values. Setting this FALSE has no effect. There is no default. |
|
All objects |
INHERIT |
BOOLEAN |
If TRUE, inherits session-level parameters. Defaults to FALSE. If an application calls ADD_TRANSFORM to add the DDL transform, then by default the only transform parameters that apply are those explicitly set for that transform handle. This has no effect if the transform handle is the session transform handle. |
|
ROLE |
REVOKE_FROM |
Text |
The name of a user from whom the role must be revoked. If this is a non-null string and if the CREATE ROLE statement grants you the role, aREVOKE statement is included in the DDL after the CREATE ROLEstatement. Note: When you issue a CREATE ROLE statement, Oracle may grant you the role. You can use this transform parameter to undo the grant. Defaults to null string. |
|
TABLESPACE |
REUSE |
BOOLEAN |
If TRUE, include the REUSE parameter for datafiles in a tablespace to indicate that existing files can be reused. If FALSE, omit the REUSEparameter. Defaults to FALSE. |
|
CLUSTER, INDEX,ROLLBACK_SEGMENT, TABLE,TABLESPACE |
PCTSPACE |
NUMBER |
A number representing the percentage by which space allocation for the object type is to be modified. The value is the number of one-hundreths of the current allocation. For example, 100 means 100%. If the object type is TABLESPACE, the following size values are affected: - in file specifications, the value of SIZE - MINIMUM EXTENT - EXTENT MANAGEMENT LOCAL UNIFORM SIZE For other object types, INITIAL and NEXT are affected. |