title: How do I update a nested record in BigQuery using DML syntax?
body: <p>I've got the following BigQuery schema, and I'm trying to update the <code>event_dim.date</code> field:</p>
  
  <p><a href="https://i.stack.imgur.com/HLrBZ.png" rel="noreferrer"><img src="https://i.stack.imgur.com/HLrBZ.png" alt="enter image description here"></a></p>
  
  <p>I tried the following query using standard SQL and the new BigQuery DML:</p>
  
  <pre><code>UPDATE `sara-bigquery.examples.app_events_20170113`
  SET event_dim.date = '20170113'
  WHERE true
  </code></pre>
  
  <p>But got this error:</p>
  
  <pre><code>Error: Cannot access field date on a value with type ARRAY&lt;STRUCT&lt;name STRING, params ARRAY&lt;STRUCT&lt;key STRING, 
  value STRUCT&lt;string_value STRING, int_value INT64, float_value FLOAT64, ...&gt;&gt;&gt;, timestamp_micros INT64, ...&gt;&gt; at [2:15]
  </code></pre>
  
  <p>I'm able to select the nested field with this query:</p>
  
  <pre><code> SELECT x.date FROM `sara-bigquery.examples.app_events_20170113`,
   UNNEST(event_dim) x
  </code></pre>
  
  <p>But can't figure out the correct <code>UPDATE</code> syntax.</p>