title: ga_session_id is unique identifier on Google Analytics?
body: <p>I checked the official docs here:
  <a href="https://support.google.com/firebase/answer/7061705?hl=en" rel="nofollow noreferrer">https://support.google.com/firebase/answer/7061705?hl=en</a></p>
  <p><img src="https://i.stack.imgur.com/ESTtW.png" alt="enter image description here" /></p>
  <p>But, when I checked my data, there are several user_id and user_pseudo_id in one ga_session_id.
  How is it possible?</p>
  <p><img src="https://i.stack.imgur.com/z7XPx.png" alt="enter image description here" /></p>