title: BigQuery : is it possible to iterate over an array?
body: <p>Is it possible to iterate over an array in bigquery in standard sql?</p>
  <p>Basically declare an array of strings representing table fields. ex :</p>
  <pre><code>DECLARE FIELDS_TO_CHECK ARRAY&lt;STRING&gt;;
  SET FIELDS_TO_CHECK =  ['field1', 'field2', 'field3' ];
  </code></pre>
  <p>and then iterate on this array to create requests getting percentage of non null value on this field :</p>
  <pre><code>select count(FIELD) / count(*) from 
  'table_name'`
  </code></pre>