title: how to union the tables in big query
body: <pre><code>select a,b,c from(SELECT max(modifiedtime) a FROM tabl1 ),
  (SELECT max(modifiedtime) b FROM tabl2 ),
  (SELECT max(modifiedtime) c FROM tabl3  ) ;
  </code></pre>
  
  <p>working fine but...output is like..
  Row </p>
  
  <pre><code>      a                  b              c    
  1   1421906942814      null            null  
  2   null               1421906942814   null  
  3   null               null            1421906942817
  </code></pre>
  
  <p>but I want to print data like </p>
  
  <pre><code>     a            b              c 
  1421906942814     1421906942814     1421906942817
  </code></pre>
  
  <p>how to do it...</p>