How to Diagnose and Fix the ORA-01520 Missing Required Group Number Error in Oracle

If you encounter the ORA-01520 error in Oracle, it means that a datafile has a missing group number. This error can occur for various reasons, such as a datafile being added to the wrong tablespace or a datafile being removed incorrectly. Here’s how you can diagnose and fix this issue.

Diagnosing the ORA-01520 Error

When you encounter the ORA-01520 error, the first step is to identify the affected datafile and the tablespace it belongs to. You can do this by querying the DBA_DATA_FILES view:

SELECT tablespace_name, file_name, file_id
FROM dba_data_files
WHERE file_id = <file_id>;


with the actual file_id reported in the error message.

Once you have identified the affected datafile and its tablespace, you can proceed with the following steps to fix the error.

Fixing the ORA-01520 Error

Option 1: Adding the Missing Datafile Back

If the missing group number is due to a datafile being removed incorrectly, you can add the missing datafile back to the tablespace using the following SQL command:

ALTER TABLESPACE <tablespace_name> ADD DATAFILE '<file_path>' SIZE <file_size> AUTOEXTEND ON;

Replace with the actual name of the tablespace, with the path to the datafile, and with the desired size of the datafile.

Option 2: Removing the Orphaned Datafile

If the missing group number is due to a datafile being added to the wrong tablespace, you can remove the orphaned datafile using the following SQL command:


Replace with the path to the datafile.

After executing the appropriate fix, you can verify that the error has been resolved by querying the DBA_DATA_FILES view again and checking for any remaining issues.

Additional Considerations

It’s important to note that the ORA-01520 error can also be caused by issues with the control file or the recovery catalog. If the above steps do not resolve the error, consider consulting the Oracle documentation or seeking assistance from a qualified Oracle DBA to further diagnose and fix the issue.

In conclusion, the ORA-01520 error in Oracle can be diagnosed and fixed by identifying the affected datafile and tablespace, and then adding the missing datafile back or removing the orphaned datafile as necessary. It’s important to carefully follow the steps outlined above and consider additional factors that may be contributing to the error.

I hope this guide helps you in resolving the ORA-01520 error in your Oracle database. If you have any further questions or need assistance, don’t hesitate to reach out to the Oracle community or seek professional support.

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