title: Primary key with ASC or DESC ordering?
body: <p>I'm trying to create a table with a compound primary key where the second column is ordered descending:</p>
  
  <pre><code>CREATE TABLE AccountHistory (                                                                                                                                                                           
    AccountNumber BIGINT NOT NULL,                                                                                                                                                                        
    Ts TIMESTAMP NOT NULL,                                                                                                                                                                                
    Memo TEXT,                                                                                                                                                                                            
    ChangeAmount BIGINT NOT NULL,                                                                                                                                                                         
    PRIMARY KEY (AccountNumber, ts DESC)                                                                                                                                                              
  );
  </code></pre>
  
  <p>However, PostgreSQL is saying there's a syntax error at the <code>DESC</code> clause. </p>
  
  <ul>
  <li>Does PostgreSQL really not allow this?</li>
  <li>Does it ever make sense to have a DESC key like this?</li>
  <li>Is my only option to create an additional index with my desired semantics?</li>
  </ul>