title: return member IDs who only used the business for 1 service out of many and may have used the business multiple times
body: <p>I need to return the member IDs that have used only service 'a' when a few different services are available.</p>
  
  <p>Eg. from the table the query would return member 1 and member 5 as they have only ever used service a.</p>
  
  <pre><code>memberID    service date
  1              a    1
  1              a    2
  2              a    3
  2              b    4
  3              c    5
  1              a    6
  3              c    7
  4              a    8
  4              c    9
  5              a    10
  </code></pre>