title: How to extract a spanner row into Json or Parquet format in golang?
body: <p>I'm new to golang and spanner, I want to save a snapshot of our spanner DB to Google cloud storage in every 5 mins. The format that I want to use is Parquet or JSON.</p>
  
  <pre><code>stmt = spanner.NewStatement("SELECT * FROM " + tableName + " WHERE UpdatedAt &gt;= @startDateTime AND UpdatedAt &lt;= @endDateTime")
  iter := txn.Query(ctx, stmt)
  defer iter.Stop()
  for {
      row, err := iter.Next()
      if err == iterator.Done {
          break
      }
      if err != nil {
          log.Println("Failed to read data, err = %s", err)
      }
  }
  </code></pre>
  
  <p>I have got all the rows, but I don't have a clue on how to extract all the column values and write it to a Parquet or JSON file or upload it to GCS. Is it possible to extract all the column values without knowing the type of the value or column name? Any help would be appreciated.</p>