title: Firebase search by child value
body: <p>I have the following structure on my Firebase database:
  <a href="https://i.stack.imgur.com/pnY5E.png" rel="noreferrer"><img src="https://i.stack.imgur.com/pnY5E.png" alt="firebase database"></a></p>
  
  <p>I would like to search for an user by name, last name or email but as I don't have the user key in the level above I don't know how I can achieve this. I'm doing and administrator session so it wouldn't have access to the user key.</p>
  
  <p>I have tried:</p>
  
  <pre><code>let usersRef = firebase.database().ref('users');
  usersRef.orderByValue().on("value", function(snapshot) {
      console.log(snapshot.val());
      snapshot.forEach(function(data) {
          console.log(data.key);
      });
  });
  </code></pre>
  
  <p>But it brings all the users on the database. Any ideas?</p>