title: How can I use the 'NVL' function on a result table?
body: <pre><code>select (t1.a + t2.b) sum
  from (select (aa + bb) a from table_x where cc = 'on') t1, 
       table_y t2 
  where t1.id = t2.id
  </code></pre>
  
  <p>The problem is that when t1 is not found, the final result will be null;</p>
  
  <p>How can I make the default value of t2.b to 0, when t1 is not found?</p>
  
  <p>Thx in advance.</p>