title: firebase retrieve data using orderByChild() and equalTo()
body: <p><img src="https://i.stack.imgur.com/D3Rh0.png" alt="Example my db firebase"></p>
  
  <pre><code>firebase.database().ref('requests')
    .orderByChild('sender')
    .equalTo("viePatHR0qRaBPGvsb992LEM55F3")
    .on("child_added", (snapshot) =&gt; {
      console.log(snapshot.key);})
  </code></pre>
  
  <p>So I'm trying to find the key node under "requests" in the picture: (example: <code>Mt8ElzJCDfSwDgdjjLuu38KUSw83</code> and <code>e3iFEuoTtJXAkLgOyxoT0LIeQAg1</code>)
  I used this code, But I got nothing back. What was wrong? What should I use?</p>