Well, I'm not so smart when it comes to adapting this snippet into a join with the parent table, Orders.

As soon as I join to Orders on ORDER_NUMBER, I start getting two identical rows (two lines in Order_Lines). No need to respond, separate issue, as in how to join parent and child and still return only one row when child has two or more lines associated to parent. Frustrating--this feels like a duh. More to learn!