title: Query Time execution
body: <p>Just want to ask which takes more time.</p>
  
  <p>Example scenario below:</p>
  
  <pre><code>SELECT *
  FROM 
      (SELECT * 
       FROM t1 
       WHERE [Date] BETWEEN "20151012" AND "20151018" 
  
       UNION ALL 
  
       SELECT * 
       FROM t2 
       WHERE [Date] BETWEEN "20151012" AND "20151018"
  
       UNION ALL
  
       SELECT * 
       FROM t3 
       WHERE [Date] BETWEEN "20151012" AND "20151018" 
  ) AS T
  </code></pre>
  
  <p>or this statement:</p>
  
  <pre><code>SELECT * 
  FROM 
      (SELECT * FROM t1 
  
       UNION ALL 
  
       SELECT * FROM t2 
  
       UNION ALL
  
       SELECT * FROM t3) AS T
  WHERE 
      [Date] BETWEEN "20151012" AND "20151018" 
  </code></pre>
  
  <p>Thanks a lot!</p>