title: SELECT WHERE COUNT = 1
body: <p>Table <code>LESSON</code> has fields <code>LessonDate, MemberId</code> (Among others but only these two are relevant)</p>
  <p>In English: Give me a list of the dates on which students that have only ever taken 1 class, took that class.</p>
  <p>I have tried a number of things. Here's my latest attempt:</p>
  <pre><code>SELECT LessonDate 
  FROM LESSON 
  WHERE (SELECT COUNT(MemberId) GROUP BY (MemberId)) = 1
  </code></pre>
  <p>Just keeps returning SQL errors. Obviously, the syntax and logic are off.</p>