title: Cannot connect with database link in Oracle
body: <p>I have three Oracle databases connections (XE, XE_HR and XE_SBD_HR).</p>
  
  <p>I've tried to create private database link with fixed user that connects as HR using HR password with below query on XE_SBD_HR:</p>
  
  <pre><code>CREATE DATABASE LINK DATABASE_LINK_1 CONNECT TO HR IDENTIFIED BY HR USING 'HR'; 
  </code></pre>
  
  <p>But now when I want to get data from table:</p>
  
  <pre><code>SELECT * FROM COUNTRIES@DATABASE_LINK_1;    
  
  SQL Error: ORA-12154: TNS:could not resolve the connect identifier 
  </code></pre>
  
  <p>I think this is caused by wrong database link connections because of this query response in XE_SBD_HR:</p>
  
  <pre><code>COMMIT;  
  ALTER SESSION CLOSE DATABASE LINK DATABASE_LINK_1;
  
  ORA-02081: database link is not open
  </code></pre>
  
  <p>How to fix that?</p>