title: Define new columns using other columns names
body: <p>Let’s say I have a table A with a, b, c, d columns and a query:</p>
  <pre>SELECT <br>  A.a + A.b AS sum,<br>  A.c - A.d AS difference <br>FROM A</pre>
  <p>Is there a way I could define a new column like <code>sum * difference AS product</code> inside the query? (Using the names I defined)</p>