title: Using variables in Oracle SQL Developer 3.2
body: <p>I am extremely new to SQL, and manage to extract from some other queries we use the following syntax:</p>
  
  <pre><code>--VARIABLES
  undefine PF_PROD --product;
  undefine PF_PSG --shop;
  
  
  --QUERY
  SELECT *
  FROM ET1250
  WHERE PRODUCT=&amp;&amp;PF_PROD
  AND PRICE_SHOP_GROUP=&amp;&amp;PF_PSG
  ORDER BY PERIOD_YEAR desc,PERIOD_WEEK desc;
  </code></pre>
  
  <p>This works fine as long as I run the <code>undefine</code> statements first, is there a way to make the query always ask for these variables without me having to <code>undefine</code> them first?</p>