title: "Column name id is ambiguous" error in BigQuery when I'm trying to unnest an array field
body: <p>I have a BigQuery table with schema like this (noly important fields are listed for brevity):</p>
  
  <pre><code>id [STRING]
  products [RECORD]
  products.id [STRING]
  </code></pre>
  
  <p>I'm trying to perform a query and get both id and products.id like this:</p>
  
  <pre><code>SELECT 
    id as transaction_id,
    products.id as product_id
  FROM 
    `my-project.set.transactions_table`,
    UNNEST(products) as products
  </code></pre>
  
  <p>and get an error: <code>Column name id is ambiguous at [2:3]</code></p>
  
  <p>How do I remove ambiguity here?</p>