title: Add Default Rows in Postgresql
body: <p>I want to insert default rows into a result set if the LEFT JOIN is NULL.
  For example if Jane has no roles, I want to return some default ones in the results.</p>
  <p>A query like this will return the following:</p>
  <p><code>SELECT * FROM employees  LEFT OUTER JOIN roles ON roles.employee_id = employees.id</code></p>
  <pre><code>Employee ID | Employee Name | Role ID | Role Name
  1           | John          | 1       | Admin
  1           | John          | 2       | Standard
  2           | Jane          | NULL    | NULL
  </code></pre>
  <p>I want to return:</p>
  <pre><code>Employee ID | Employee Name | Role ID | Role Name
  1           | John          | 1       | Admin
  1           | John          | 2       | Standard
  2           | Jane          | NULL    | Admin
  2           | Jane          | NULL    | Standard
  </code></pre>
  <p>Is there a good way to do this in PostgreSQL?</p>