title: Indexing a dataset if index not exist
body: <pre><code>proc sql;
  create index key on data (Date);
  &lt;other statement&gt;;
  quit;
  </code></pre>
  
  <p>I used to create index on a dataset use above syntax. But if <code>data</code> is already indexed, it will return error and will not execute <code>&lt;other statement&gt;</code>. How to ensure everytime <code>&lt;other statement&gt;</code> will be executed whether index <code>key</code> exists (if not exist, then create one)?</p>