title: NOT EXISTS in Bigquery
body: <p>I want to implement something like</p>
  
  <pre><code>select * from table1
  where not exists (select 1 from table2 where
                    table1.col1 = table2.col1 and table1.col2 = table2.col2)
  </code></pre>
  
  <p>I am not able to implement this in BQ.
  Would appreciate any help on getting this done.</p>