You can create database links to an Autonomous Database from an Oracle database that is not an Autonomous Database. For example from an on-premise Oracle database to an Autonomous Database

1. Download your Autonomous Database wallet. See Download Client Credentials (Wallets) for more information.
2. Upload the wallet to the database instance where you want to create the link to the Autonomous Database.
3. Unzip the Autonomous Database wallet:
   Note
   
   The wallet file, along with the Database user ID and password provide access to data in your Autonomous Database. Store wallet files in a secure location. Share wallet files only with authorized users.

   [oracle@sys1 ~]$ cd/u01/targetwallet
   [oracle@sys1 targetwallet]$ unzip Wallet_name1.zip
           Archive: Wallet_name1.zip  
             inflating: cwallet.sso
             inflating: tnsnames.ora    
             inflating: truststore.jks            
             inflating: ojdbc.properties          
             inflating: sqlnet.ora
             inflating: ewallet.p12
             inflating: keystore.jks
   

4. Set GLOBAL_NAMES to FALSE.

   SQL> ALTER SYSTEM SET GLOBAL_NAMES = FALSE;
    
   System altered.
   
   SQL> SHOW PARAMETER GLOBAL_NAMES
   NAME                     TYPE        VALUE
   ----------------------   ----------- -----------
   global_names             boolean     FALSE
   

   Set GLOBAL_NAMES to FALSE to use a database link name without checking that the name is different than the remote database name.When GLOBAL_NAMES, is set to TRUE, the database requires the database link to have the same name as the database to which it connects. See GLOBAL_NAMES for more information.

5. Create the database link to the target Autonomous Database. Note that the security path includes my_wallet_directory; the path where you unzip the Autonomous Database wallet.

   CREATE DATABASE LINK ADBLINK 
      CONNECT TO NAME1 IDENTIFIED BY ************ 
      USING
   '(description=(retry_count=20)(retry_delay=3)
        (address=(protocol=tcps)(port=1522)(host=example1.oraclecloud.com))     
        (connect_data=(service_name=example2_high.adb.oraclecloud.com))     
        (security=(my_wallet_directory=/u01/targetwallet)
           (ssl_server_dn_match=true)))';
   
   Database link created.

6. Use the database link you created to access data on the target database (your Autonomous Database instance in this case):

   For example:

   SELECT * FROM employees@ADBLINK;