title: Refer to a column name alias in the WHERE clause
body: <p>I have written down this query in postgres sql with column alias it is working fine:</p>
  
  <pre><code>select email as e from users 
  </code></pre>
  
  <p>It displays me result under <code>e</code> column alias but when I fire <code>where</code> condition with <code>e</code> then it shows this error:</p>
  
  <pre><code>select email as e from users where e = 'jaskaransingh@demo.com'
  </code></pre>
  
  <blockquote>
    <p>ERROR:  column "e" does not exist</p>
  </blockquote>
  
  <p>Why so? How we can use alias in where condition?</p>