Use remap when you don't want to replace existing schema

You might be taking periodic backups of your database and might need to restore backups as well. In such situations, if you do not need to overwrite existing data remap command can be used with impdp.There are options only to restore a specific set of tables. In here I will show how to restore the whole schema without replacing the existing.

1. First it is required a directory to be created so that all the exports stored in that directory and all the import dumps also will be read from the same. 
Follow this to create the directories and grant access.

2. Then lets create a backup of an existing schema. I've explained the backing-up procedure here. Else you can use following.
EXPDP X/X SCHEMAS=SCHEMA(S)_TO_IMPORT DUMPFILE=DUMPFILE_TO_IMPORT_FROM

e.g

expdp spfix/spfix schemas=spfix dumpfile=spfix_030812.dmp 

3. Now, our plan is to restore the dump on a new schema. So lets create a new user and grant access.

SQL> Create user yumani identified by yumani account unlock;

User created.

SQL> grant create session, dba to yumani;

Grant succeeded.

SQL> grant connect to yumani;

Grant succeeded.

  3. Let's restore the backup

Use this command to restore the backup using the schema you created above,
IMPDP REMAP_SCHEMA=OLD_OWNER:NEW_OWNER  DUMPFILE=DUMFILE.DMP NOLOGFILE=Y 

e.g

impdp yumani/yumani@daniddb schemas=yumani remap_schema=yumani:yumani1 dumpfile=yumani_120812.dmp NOLOGFILE=Y