title: Querying for tag values in a given list
body: <p>Is there any shortform syntax in influxdb to query for membership in a list? I'm thinking of something along the lines of </p>
  
  <pre><code>SELECT * FROM some_measurement WHERE some_tag IN ('a', 'b', 'c')
  </code></pre>
  
  <p>For now I can string this together using <code>OR</code>ed <code>=</code>s, but that seems very inefficient. Any better approaches? I looked through the <a href="https://influxdb.com/docs/v0.9/query_language/spec.html" rel="noreferrer">language spec</a> and I don't see this as a possibility in the expression productions.</p>
  
  <p>Another option I was thinking was using the regex approach, but that seems like a worse approach to me.</p>