title: Can't modify a table to add a foreign key
body: <p>I have 2 tables</p>
  
  <ul>
  <li><code>Songs</code> (SONGID, SONGNAME, ALBUM, ARRANGER, VOCALISTS, LYRCISTS)</li>
  <li><code>Source_songs</code> (Source_Song_Name, ID_ACTUALSONGNAME) </li>
  </ul>
  
  <p>and I can't modify <code>Songs</code> to add a foreign key</p>
  
  <pre><code>ALTER TABLE SONGS
     ADD CONSTRAINT Original_Song_Name
     ADD FOREIGN KEY (Source_song_id)                 
         REFERENCES Source_SongName (SOURCE_SONGNAME);
  </code></pre>
  
  <p>And I get this error. I know I'm spelling the column name right idk what to do.</p>
  
  <p>Error:</p>
  
  <blockquote>
    <p>SQL Error: ORA-00904: : invalid identifier<br>
    00904. 00000 -  "%s: invalid identifier"</p>
  </blockquote>