Error
Error Code: ORA-28451

Oracle ORA-28451: Incomplete Database Link

📦 Oracle Database
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Description

The ORA-28451 error indicates an incomplete ALTER DATABASE LINK statement. This occurs when attempting to reset a shared database link password without specifying the necessary CONNECT TO, AUTHENTICATED BY, or IDENTIFIED BY clauses.
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Error Message

ORA-28451: incomplete ALTER DATABASE LINK statement
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Known Causes

3 known causes
⚠️
Missing CONNECT TO Clause
The CONNECT TO clause, specifying the user to connect as, is absent from the ALTER DATABASE LINK statement. 🔒
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Missing AUTHENTICATED BY Clause
The AUTHENTICATED BY schema_name clause, specifying the schema for authentication, is missing. 🔒
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Missing IDENTIFIED BY Clause
The IDENTIFIED BY password clause, crucial for resetting the password, is not included in the statement. 🔒
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Solutions

3 solutions available

1. Complete the ALTER DATABASE LINK Statement easy

Ensure all necessary clauses are present when altering a database link.

1
Identify the database link that is causing the error. You can usually find this information in the error stack or by examining recent DDL statements.
2
Review the `ALTER DATABASE LINK` syntax. The error `ORA-28451` typically occurs when the statement is not fully formed. Common missing clauses include `CONNECT TO` and `USING`.
ALTER DATABASE LINK <dblink_name>
CONNECT TO <username> IDENTIFIED BY <password>
USING '<tns_entry_or_connect_string>';
3
Re-execute the `ALTER DATABASE LINK` statement with all required clauses. For example, to change the connecting user and password:
ALTER DATABASE LINK MY_REMOTE_DB
CONNECT TO NEW_USER IDENTIFIED BY new_password
USING 'REMOTE_SERVICE';
-- Or to change the connect string:
ALTER DATABASE LINK MY_REMOTE_DB
CONNECT TO EXISTING_USER IDENTIFIED BY existing_password
USING 'NEW_REMOTE_SERVICE';
-- Or to simply re-establish the link with existing credentials:
ALTER DATABASE LINK MY_REMOTE_DB CONNECT TO CURRENT_USER USING 'CURRENT_TNS_ENTRY';

2. Drop and Recreate the Database Link easy

If the existing database link is corrupted or difficult to correct, dropping and recreating it is a reliable solution.

1
Connect to the local database where the database link is defined using a privileged user (e.g., SYS or a user with CREATE DATABASE LINK privileges).
2
Drop the existing database link:
DROP DATABASE LINK <dblink_name>;
3
Recreate the database link with the correct syntax, ensuring all necessary clauses are included:
CREATE DATABASE LINK <dblink_name>
CONNECT TO <username> IDENTIFIED BY <password>
USING '<tns_entry_or_connect_string>';
4
Verify the database link by trying to query a table on the remote database:
SELECT COUNT(*) FROM dual@<dblink_name>;

3. Verify TNSNAMES.ORA Configuration medium

An incomplete or incorrect TNSNAMES.ORA entry can lead to issues with database link creation/alteration.

1
Locate the `tnsnames.ora` file on the Oracle client or server where the database link is being managed. The location can vary but is often found in `$ORACLE_HOME/network/admin` or specified by the `TNS_ADMIN` environment variable.
2
Examine the entry for the TNS alias used in your `USING` clause of the database link. Ensure it is complete and correctly formatted. An incomplete entry might look like this:
REMOTE_SERVICE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = remote_host)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = remote_service_name)
    )
  )
3
If the TNS entry is incomplete or missing, correct it. For example, ensure `SERVICE_NAME` or `SID` is present.
REMOTE_SERVICE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = remote_host)(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = remote_service_name)  -- Ensure this is present and correct
    )
  )
4
After correcting `tnsnames.ora`, test the connection using `tnsping` from the command line on the server or client where the `tnsnames.ora` file resides:
tnsping <tns_entry_or_connect_string>
5
Once `tnsping` is successful, re-attempt the `ALTER DATABASE LINK` statement.
ALTER DATABASE LINK <dblink_name>
CONNECT TO <username> IDENTIFIED BY <password>
USING '<tns_entry_or_connect_string>';