title: Average Quantity with subselect
body: <p>I have following table, where OrderID is unique and ordernumber is not unique:</p>
  <pre><code>OrderID|Ordernumber|ProductID|Quantity
  1|1234|10|12|
  2|1234|55|10|
  3|1234|55|22|
  4|1029|99|44|
  </code></pre>
  <p>1.I want complete table and using subselect to get average quantity per ordernumber , but as far I know subselect only allows one Column.</p>
  <p>And another query where the avg is per Ordernumber and per Prod</p>
  <pre><code>OrderID|Ordernumber|ProductID|AVGQuantity
  1|1234|10|14,7|
  2|1234|55|14,7|
  3|1234|55|14,7|
  4|1029|99|44|
  </code></pre>
  <p>Outcome should be:</p>
  <pre><code>OrderID|Ordernumber|ProductID|AVGQuantity
  1|1234|10|11|
  2|1234|55|11|
  3|1234|55|22|
  4|1029|99|44|
  </code></pre>
  <p>Thanks in advance.</p>