title: BigQuery Standard SQL - querying 3 different tables with same schema. How to add column with what table each row is from?
body: <p>Say I have 3 tables containing clothing brands from - walmart, target, amazon.
  I make a new table and query * from each table into this new table. I want to know which company (walmart, target or amazon) each of these items is from. How would I go about doing this in BigQuery?</p>
  <p>Thank you.</p>