title: Keeping a nested structure in a result table while writing over nested data
body: <p>I need to do some brief masking of data in our bigquery table. I need the resulting table to have the same structure, but removed of personal information.</p>
  
  <p>I'm doing something along the lines of:</p>
  
  <pre><code>select
  customer,
  "1234 Road" as tttt.address
  ...
  from table
  </code></pre>
  
  <p>I can't delve into more detail, but I need to overwrite things such as customer name and phone number, while the structure remains the same. </p>