title: SELECT DISTINCT or SELECT efficiency for IN clause
body: <p>Using Oracle (if that matters).  Both of these Select statements will produce the same end result, but which one is quicker?</p>
  
  <pre><code>SELECT * FROM tbl_A WHERE val IN (SELECT myField FROM tbl_B WHERE ... );
  </code></pre>
  
  <p>or would a SELECT DISTINCT in the sub-query be better?</p>
  
  <pre><code>SELECT * FROM tbl_A WHERE val IN (SELECT DISTINCT myField FROM tbl_B WHERE ... );
  </code></pre>
  
  <p>Thanks!</p>