title: SAS PROC SQL - How to compute date difference
body: <p>I'm using SAS with SQL procedures.
  I need to compute a field as a date difference from today, ex the number of days from the birth date.</p>
  
  <pre><code>PROC SQL;
  CREATE TABLE myTable AS
  SELECT BIRTH_DATE, &lt;some function&gt; AS DAYS_BETWEEN_BIRTHDATE_AND_TODAY
  FROM someTable
  </code></pre>
  
  <p>What's the best way to do this and what if I want to compute monthly difference or yearly difference?</p>