title: Union ALL multiple query Google BigQuery
body: <p>I have three queries with the same column count and structure, does Google BigQuery support union all? I know it supports union but I need it to merge the result of the query into one result.</p>
  
  <p>I have tried:</p>
  
  <pre><code>SELECT * 
  FROM 
  (SELECT a.a AS a, a.b AS b, d.c AS c FROM table_a a JOIN table_d d on d.a = a.a),
  (SELECT c.a AS a, c.b AS b, d.c AS c FROM table_c c JOIN table_d d on d.a = ca.a),
  (SELECT b.a AS a, b.b AS b, d.c AS c FROM table_b b JOIN table_d d on d.a = b.a)
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Union results in ambiguous schema [d.c] is ambiguous and is aliasing multiple fields
  </code></pre>
  
  <p>Thanks For your help.</p>