Select all records where ID appears once SQL
<p>I have a table of the form: </p>

<pre><code>User1 A
User2 A
User2 B
User3 C
User4 A
User4 C
User5 D
</code></pre>

<p>and out of this I need to pick <strong>ONLY the users who appear once</strong>. So for example, from the above I want User1, User3, User5. I could use something like <code>row_number()</code> to remove duplicates, however this would return one row for all users, even those who have more than 1 entry, which is not what I want. I can't use <code>DISTINCT</code> either as for example <code>User2 A</code> and <code>User2 B</code> would not be caught as they are not equal.  </p>