title: SQL question from Joel Spolsky article
body: <p>From Joel Spolsky's  <a href="http://www.joelonsoftware.com/articles/LeakyAbstractions.html" rel="noreferrer">article</a> on leaky abstractions:</p>
  
  <blockquote>
    <p>[C]ertain SQL queries are thousands of times slower than other logically equivalent queries. A famous example of this is that some SQL servers are dramatically faster if you specify "where a=b and b=c and a=c" than if you only specify "where a=b and b=c" even though the result set is the same.</p>
  </blockquote>
  
  <p>Does anyone know the details of this?</p>