title: BigQuery accessing CustomDimensions with new SQL syntax
body: <p>I am migrating to the new SQL syntax in BigQuery, since it seems more flexible. However I am a bit stuck when it comes to access the fields in the customDimensions. I am writing something quite simple like this:</p>
  
  <pre><code>SELECT 
    cd.customDimensions.index,
    cd.customDimensions.value
  FROM `xxxxx.ga_sessions_20170312`, unnest(hits) cd
  limit 100
  </code></pre>
  
  <p>But I get the error</p>
  
  <pre><code>Error: Cannot access field index on a value with type ARRAY&lt;STRUCT&lt;index INT64, value STRING&gt;&gt;
  </code></pre>
  
  <p>However if I run something like this works perfectly fine:</p>
  
  <pre><code>    SELECT 
          date,
          SUM((SELECT SUM(latencyTracking.pageLoadTime) FROM UNNEST(hits))) pageLoadTime,
          SUM((SELECT SUM(latencyTracking.serverResponseTime) FROM UNNEST(hits))) serverResponseTime
     FROM `xxxxxx.ga_sessions_20170312`
      group by 1
  </code></pre>
  
  <p>Is there some different logic when it comes to query the customDimensions?</p>