title: Updating historical data by joining another table
body: <p>I have a BigQuery table A(simplified version below) that is updated with a daily scheduled query. Last week we added a new column - ad_number - to the table. Going forward, ad_number will be populated with data. However, I would like to pull the historical data from last year, for this column.</p>
  <pre><code>Event_date (dimension)
  App_id (dimension)
  Country (dimension)
  Ad_network (dimension)
  Total_revenue (metric)
  Ad_number (metric)
  </code></pre>
  <p>Because of the large data volume, I've created a separate table B with the same dimensions and ad_number, to pull from the source table indicated in the scheduled query. I plan on joining this into Table A. Any tips on how to do this?</p>
  <p>Thank you in advance!</p>