title: Updating Inventory table from Sales table
body: <p>Hey all so I have 2 tables. </p>
  
  <p>Inventory:</p>
  
  <pre><code>ITEMNAME | QUANTITY
  ---------|---------
  ITEM A   |       200
  ITEM B   |       310
  ITEM C   |       255
  ITEM D   |       115
  </code></pre>
  
  <p>Sales:</p>
  
  <pre><code>SALENO | QUANTITY | ITEMNAME
  -------|----------|---------
  1001   |         5|   ITEM A
  1002   |       100|   ITEM X
  1003   |         1|   ITEM C
  1004   |        20|   ITEM B
  </code></pre>
  
  <p>What I am having trouble with is updating my Inventory QUANTITY values with specific SALENOs. </p>
  
  <p>Lets say I have already UPDATED my Inventory up to SALENO 1002. </p>
  
  <p>So SALENO 1003 &amp; 1004 are new sales and so I only need to subtract from my Inventory QUANTITY those 2 specific orders. How can I achieve this? </p>
  
  <p>Any advice is appreciated. Thanks!</p>