title: How to sort customer names by items purchased in SQL
body: <p>Sorry new to this but,</p>
  <p>I need to sort customer names by total quantity of items purchased by them, in desc order.
  the purchased amount in the table is known as Inv_number</p>
  <p>I would need the customer name and than the sum. This is what it should be
  <img src="https://i.stack.imgur.com/Lr0Vw.png" alt="enter image description here" /></p>
  <p>Thanks</p>