ORA-01113: file string needs media recovery

Question:  I get this error when starting my Oracle database.  What is the ORA-01113 error?

SQL> ALTER TABLESPACE sample
 ONLINE  2  ;
ALTER TABLESPACE sample
*
ERROR at line 1:
ORA-01113: file 27 needs media recovery
ORA-01110: data file 27: '/u02/oracle/oradata/ORCL/sample.dbf'


SQL> recover datafile '/u02/oracle/oradata/ORCL/sample.dbf';
Media recovery complete.
SQL> ALTER TABLESPACE sample ONLINE;
ALTER TABLESPACE sample ONLINE
*
ERROR at line 1:
ORA-01113: file 29 needs media recovery
ORA-01110: data file 29: '/u02/oracle/oradata/ORCL/SAMPLE10.dbf'


SQL> recover datafile '/u02/oracle/oradata/ORCL/SAMPLE10.dbf';
Media recovery complete.
SQL> ALTER TABLESPACE sample ONLINE;
ALTER TABLESPACE sample ONLINE
*
ERROR at line 1:
ORA-01113: file 30 needs media recovery
ORA-01110: data file 30: '/u01/app/QPDEV/SAMPLE11.dbf'


SQL> recover datafile '/u01/app/QPDEV/SAMPLE11.dbf';
Media recovery complete.
SQL> ALTER TABLESPACE sample ONLINE;

Tablespace altered.

The ORA-01113 error can be thrown when you begin to start Oracle with the "startup" command. or sometimes if u take Tablespace offline and try to bring it back online.

 The ORA-01113 has many causes: