title: select multiple column from one table and insert into another as rows
body: <p>I have two tables users and emails:</p>
  
  <pre><code>USER
  +--------+-------+--------+--------+
  | id (PK)| email | email2 | email3 |
  +--------+-------+--------+--------+
  
  EMAIL
  +---------+--------------+---------------+
  | id (PK) | user_id (FK) | email_address | 
  +---------+--------------+---------------+
  </code></pre>
  
  <p>I need to select emails from users table and insert them into emails table as rows.</p>