title: Join 2 tables, sum and group by
body: <p>Should be fairly simple but I am new to SQL and can't get it to work :</p>
  
  <pre><code>Table 1:
  ID        Qty
  ItemA     3 
  ItemB     5  
  ItemD     2 
  
  Table 2:
  ID        Qty
  ItemC    -1
  ItemB    1.5 
  ItemE     2.2
  </code></pre>
  
  <p>I just  want one table with the Quantities summed by ID. </p>