title: Join string and add character between them in mysql
body: <p>I have two tables as below:</p>
  
  <p><strong>agents</strong></p>
  
  <pre><code>id    |  name
  1     |  abc
  2     |  def
  </code></pre>
  
  <p><strong>stores</strong></p>
  
  <pre><code>id | name | agent_id
  1  | aaa  | 1
  2  | bbb  | 1
  </code></pre>
  
  <p><strong>I want to result like this:</strong></p>
  
  <pre><code>agent_name | store_name
    abc      | aaa|bbb
  </code></pre>
  
  <p><strong>Not:</strong></p>
  
  <pre><code>agent_name | store_name
    abc      |   aaa
    abc      |   bbb
  </code></pre>
  
  <p>Which query can help me do this? I know <code>concat</code> function but I don't know how to add characters <code>|</code> between strings. </p>