title: Write a Postgres Get or Create SQL Query
body: <p>I want to write a single Postgres SQL statement that says look for a user with color X and brightness Y.  If that user exists, return all of its row data.  If not, create a new row and pass additional information.  The two separate statements would do something like this:</p>
  
  <pre><code>Select (color, brightness, size, age) FROM mytable WHERE color = 'X' AND brightness= 'Y';
  </code></pre>
  
  <p>If that doesn't return anything, then execute this:</p>
  
  <pre><code>INSERT INTO mytable (color, brightness, size, age) VALUES (X, Y, big, old);
  </code></pre>
  
  <p>Is there a way to combine these into a single query??</p>