title: UNION ALL and LIMIT in MySQL
body: <p>Let's say I want to perform this query:  </p>
  
  <pre><code>(SELECT a FROM t1 WHERE a=10 AND B=1) 
  UNION ALL 
  (SELECT a FROM t2 WHERE a=11 AND B=2) 
  UNION ALL 
  (SELECT a FROM t3 WHERE a=12 AND B=3) 
  ORDER BY a LIMIT 1000;
  </code></pre>
  
  <p>Is MySQL smart enough to skip "t3" if 550 results are available in "t1" and 450 in "t2"? </p>
  
  <p>I'm looking at MySQL docs (<a href="http://dev.mysql.com/doc/refman/5.1/en/union.html" rel="noreferrer"><a href="http://dev.mysql.com/doc/refman/5.1/en/union.html" rel="noreferrer">http://dev.mysql.com/doc/refman/5.1/en/union.html</a></a>) but can't seem to find the answer.</p>