title: How to perform join query in Firebase?
body: <p>After retrieving group key in HashMap how to perform join query which shows only those <code>grp</code> details which have member as that particular user. And if this structure is wrong please help me with this.</p>
  
  <p>Structure:</p>
  
  <p><img src="https://i.stack.imgur.com/Faqkn.png" alt="screenShot"></p>