Join 2 tables by matching children - sql-server

Question

I'm trying to have 2 tables (In this case it's actually 1 table in a self join) joined by their matching children.
Let me preface the purpose of this which might give a better understanding what I need:
I'm trying to look up a new order that I just got, to see if we ever had the same order, in order to find out in which box type this would be packaged.
So i'd need the matching order to contain the same item and the same qty for the item.
Look at the tables below and note that order 1300981 has the same items as order 1303097, how do I write this join?
Remember: I don't want the results to include any matches that do not match %100.
SQL Fiddle
OrderMain:
| OrderID | BoxId |
|---------|--------|
| 1300981 | 34 |
| 1303096 | (null) |
| 1303097 | (null) |
| 1303098 | (null) |
| 1303099 | (null) |
| 1303100 | (null) |
| 1303101 | (null) |
| 1303102 | (null) |
| 1303103 | (null) |
| 1303104 | B1 |
| 1303105 | (null) |
| 1303106 | (null) |
| 1303107 | 48 |
| 1303108 | (null) |
| 1303109 | (null) |
| 1303110 | (null) |
| 1303111 | (null) |
| 1303112 | (null) |
| 1303113 | (null) |
| 1303114 | (null) |
| 1303115 | (null) |
| 1303116 | (null) |
| 1303117 | (null) |
Order Detail:
| id | OrderID | Item | Qty |
|----|---------|--------|-----|
| 1 | 1300981 | 172263 | 3 |
| 2 | 1300981 | 171345 | 3 |
| 3 | 1300981 | 138757 | 3 |
| 4 | 1303117 | 231711 | 1 |
| 5 | 1303116 | 227835 | 1 |
| 6 | 1303115 | 244798 | 1 |
| 7 | 1303114 | 121755 | 1 |
| 8 | 1303113 | 145275 | 2 |
| 9 | 1303112 | 219554 | 1 |
| 10 | 1303111 | 179385 | 1 |
| 11 | 1303110 | 6229 | 1 |
| 12 | 1303109 | 217330 | 1 |
| 13 | 1303108 | 243596 | 1 |
| 14 | 1303107 | 246758 | 1 |
| 15 | 1303106 | 193931 | 1 |
| 16 | 1303105 | 244659 | 1 |
| 17 | 1303104 | 192548 | 1 |
| 18 | 1303103 | 228410 | 1 |
| 19 | 1303102 | 147474 | 1 |
| 20 | 1303101 | 239191 | 1 |
| 21 | 1303100 | 243594 | 1 |
| 22 | 1303099 | 232301 | 1 |
| 23 | 1303098 | 201212 | 1 |
| 24 | 1303097 | 172263 | 3 |
| 25 | 1303097 | 171345 | 3 |
| 26 | 1303097 | 138757 | 3 |
| 27 | 1303096 | 172263 | 3 |
| 28 | 1303096 | 171345 | 1 |
| 29 | 1303096 | 138757 | 3 |
| 30 | 1303095 | 172263 | 3 |
Expected Results
| OrderID | BoxId |
|---------|--------|
| 1303097 | 34 |

Answer 1

May be a weird way to do this, but if you convert the order details to xml and compare it to other orders, you can look for matches.
WITH BoxOrders AS
(
SELECT om.[OrderId],
om.[BoxId],
(SELECT Item, Qty
FROM orderDetails od
WHERE od.[OrderId] = om.[OrderId]
ORDER BY Item
FOR XML PATH('')) Details
FROM orderMain om
WHERE BoxID IS NOT NULL
)
SELECT mo.OrderId, bo.BoxId
FROM BoxOrders bo
JOIN (
SELECT om.[OrderId],
om.[BoxId],
(SELECT Item, Qty
FROM orderDetails od
WHERE od.[OrderId] = om.[OrderId]
ORDER BY Item
FOR XML PATH('')) Details
FROM orderMain om
WHERE BoxID IS NULL
) mo ON bo.Details = mo.Details

Answer 2

SQL Fiddle
Here's a different approach using SQL and a few analytics.
This joins order detail to itself based on item and qty and order number < other order number and ensures the count of items in each order matches. Thus if items match, count matches and qty matches then the order has the same items.
This returns both orders but easily enough to adjust. Using the CTE so the count materializes. Pretty sure you can't use a having with an analytic like this.
The one major assumption I'm making is that order numbers are sequential and when you say see if an older order exists, I should only need to look at earlier order numbers when evaluating if a prior order had the same items and quantities.
I'm also assuming a 100% match means: Exact same items. Same Quantity of items. and SAME Item Count so count of items for order 1 is 3 and order 2 is 3 and items and quantities match that is 100% but if order 2 had 4 items and order 1 only had 3, no match.
with cte as (
SELECT distinct OD1.OrderID PriorOrder, od2.orderID newOrder, OM.BoxId,
count(OD1.Item) over (partition by OD1.OrderID) OD1Cnt,
count(OD2.Item) over (partition by OD2.OrderID) OD2cnt
FROM OrderDetails OD1
INNER JOIN orderDetails OD2
on OD1.item=OD2.item
and od1.qty = od2.qty
and OD1.OrderID < OD2.OrderID
LEFT JOIN ORderMain OM
on OM.OrderID = OD1.orderID)
Select PriorOrder, NewOrder, boxID from cte where od1cnt = od2cnt