title: sum result is being multiplied by number of rows
body: <p>I'm trying to get 2 sums from my tables, one is a table of ordered items and another is a table of received items. With my current query i'm getting a sum of 2014 which is from 106(the actual sum I want to get) multiplied by 19(the number of records)</p>
  
  <pre><code>select POD.PO_No, SUM(POD.Qty) as Qty, RRD.RR_No, SUM(RRD.QtyRcvd) as QtyReceived
  from tbl_PODetail POD inner join tbl_RRDetail RRD on POD.PO_No = RRD.PO_Reference
  where POD.PO_No = 'PO-000001'
  group by POD.PO_No, RRD.RR_No
  </code></pre>
  
  <p>What causes this and how can I correct it?</p>
  
  <p>Sample Table</p>
  
  <pre><code>PO No      | Item   | Qty
  -------------------------
  PO-0000001 | Item A | 5
  PO-0000001 | Item B | 7
  PO-0000001 | Item B | 3
  
  RR No      | Item   | Qty | PO_Reference
  ----------------------------------------
  RR-0000001 | Item A | 5   | PO-0000001
  RR-0000001 | Item B | 7   | PO-0000001
  RR-0000001 | Item B | 3   | PO-0000001
  </code></pre>
  
  <p>Expected Output:</p>
  
  <pre><code>PO No      | Qty | RR No      | Qty Rcvd
  -----------------------------------------
  PO-0000001 | 15  | RR-0000001 |  15
  </code></pre>
  
  <p>What I get</p>
  
  <pre><code>PO No      | Qty | RR No      | Qty Rcvd
  -----------------------------------------
  PO-0000001 | 45  | RR-0000001 |  45
  </code></pre>