title: PostgreSQL create table if not exists
body: <p>In a MySQL script you can write:</p>
  
  <pre><code>CREATE TABLE IF NOT EXISTS foo ...;
  </code></pre>
  
  <p>... other stuff ...</p>
  
  <p>and then you can run the script many times without re-creating the table.</p>
  
  <p>How do you do this in PostgreSQL?</p>