impdp 字符集&外键&OID

imp导入时候经常遇到一些问题
1，字符集问题
   如果原库字符集是GBK，目标字符集是UTF-8，则原库中文是占用2个字符，目标库是3个字符，有些列
  会发生长度不够问题
2，外键依赖
   有问题1引起或者别的问题，比如导入次序问题
解决：
a，导入元数据
导入选项加入CONTENT=METADATA_ONLY
b,禁用外键&修改某些列长度
 约束：
 SELECT 'ALTER TABLE ' || TABLE_NAME || ' DISABLE CONSTRAINT ' || constraint_name || ';'
 FROM user_constraints
 WHERE CONSTRAINT_TYPE = 'R';
 修改列长度，这个要查询那些列需要扩充
3，导入数据
 导入选项CONTENT=DATA_ONLY
4，启用约束
 SELECT 'ALTER TABLE ' || TABLE_NAME || ' ENABLE CONSTRAINT ' || constraint_name || ';'
 FROM user_constraints
 WHERE CONSTRAINT_TYPE = 'R';

3，oid已经存在问题
ORA-39083: Object type TYPE failed to create with error:
ORA-02304: invalid object identifier literal

mpdp导入对象时候失败，说明目标库中已经存在一个oid为XXX的对象，参看impdp的帮助：
TRANSFORM
Metadata transform to apply to applicable objects.
Valid transform keywords: SEGMENT_ATTRIBUTES, STORAGE OID, and PCTSPACE.
 
OID - If the value is specified as n, the assignment of the exported OID during the
creation of object tables and types is inhibited. Instead, a new OID is assigned.
This can be useful for cloning schemas, but does not affect referenced objects. The
default value is y.
导入时候设置transform=oid:n即可，oid在克隆schema时候使用