title: How to extract all the keys in a JSON object with BigQuery
body: <p>BigQuery has facilities to parse JSON in real-time interactive queries: Just store the JSON encoded object as a string, and query in real time, with functions like JSON_EXTRACT_SCALAR.</p>
  
  <p>However, I can't find a way to discover all the keys (properties) in these objects. </p>
  
  <p>Can I use a UDF for this?</p>