title: Generate sequence numbers on PostgreSQL integer column
body: <p>I have a table on PostgreSQL and 1000 rows in it. I have an integer column in my table that is empty. I want to populate <code>newid</code> with sequential, unique numbers a bit like a primary key.</p>
  
  <pre><code>Product
  -------------------------
  id  name  newid  size
  60   ....  null   L
  72   ....  null   M
  83   ....  null   xl
  84   ....  null   S
  85   ...
  </code></pre>
  
  <p>How can I write a query that update my <code>newid</code> column.</p>
  
  <pre><code>Product
  -------------------------
  id  name  newid  size
  60   ....  1      L
  72   ....  2      M
  83   ....  3      xl
  84   ....  4      S
  85   ...
  </code></pre>