SQL Server: FOR XML PATH - nidificazione/raggruppamento

Question

Ho dati che assomiglia:

OrderID CustomerID ItemID ItemName 
10000 1234  111111 Product A 
10000 1234  222222 Product B 
10000 1234  333333 Product C 
20000 5678  111111 Product A 
20000 5678  222222 Product B 
20000 5678  333333 Product C 

Voglio scrivere una query T-SQL in SQL Server per restituire i dati in questo modo:

<Root> 
    <Order> 
    <OrderID>10000</OrderID> 
    <CustomerID>1234</CustomerID> 
    <LineItem> 
     <ItemID>11111</ItemId> 
     <ItemName>Product A</ItemName> 
    </LineItem> 
    <LineItem> 
     <ItemID>22222</ItemId> 
     <ItemName>Product B</ItemName> 
    </LineItem> 
    <LineItem> 
     <ItemID>33333</ItemId> 
     <ItemName>Product B</ItemName> 
    </LineItem> 
    </Order> 
    <Order> 
    <OrderID>20000</OrderID> 
    <CustomerID>5678</CustomerID> 
    <LineItem> 
     <ItemID>11111</ItemId> 
     <ItemName>Product A</ItemName> 
    </LineItem> 
    <LineItem> 
     <ItemID>22222</ItemId> 
     <ItemName>Product B</ItemName> 
    </LineItem> 
    <LineItem> 
     <ItemID>33333</ItemId> 
     <ItemName>Product B</ItemName> 
    </LineItem> 
    </Order> 
</Root> 

ho provato tornando la query in XML utilizzando:

FOR XML PATH ('Order'), root ('Root') 

Ma che mi dà un nodo Order per ogni riga (6 in totale) vs. solo un nodo ordine per ogni orderId (2 in totale).

Qualche idea?

Answer 1

select 
    OrderID, 
    CustomerID, 
    (
     select 
     ItemID, 
     ItemName 
     from @Orders rsLineItem 
     where rsLineItem.OrderID = rsOrders.OrderID 
     for xml path('LineItem'), type 
    ) 
from (select distinct OrderID, CustomerID from @Orders) rsOrders 
FOR XML PATH ('Order'), root ('Root') 

Answer 2

di esecuzione: qui è una soluzione senza selezione secondaria, che dovrebbero eseguire più veloce per i grandi tavoli. Invece i gruppi la tavola come tante volte quanti sono i livelli nel XML e identifica il livello con GROUPING_ID (vedi https://technet.microsoft.com/en-us/library/bb522495(v=sql.105).aspx e https://docs.microsoft.com/en-us/sql/relational-databases/xml/use-explicit-mode-with-for-xml):

with rsOrders as (
    select '10000' OrderID, '1234' CustomerID, '111111' ItemID, 'Product A' ItemName union 
    select '10000' orderId, '1234' customerID, '222222' itemID, 'Product B' ItemName union 
    select '10000' orderId, '1234' customerID, '333333' itemID, 'Product C' ItemName union 
    select '20000' orderId, '5678' customerID, '111111' itemID, 'Product A' ItemName union 
    select '20000' orderId, '5678' customerID, '222222' itemID, 'Product B' ItemName union 
    select '20000' orderId, '5678' customerID, '333333' itemID, 'Product C' ItemName 
) 
select case 
     when GROUPING_ID(ItemID) = 0 then 3 
     when GROUPING_ID(OrderID) = 0 then 2 
     else 1 
     end as tag, 
     case 
      when GROUPING_ID(ItemID) = 0 then 2 
     when GROUPING_ID(OrderID) = 0 then 1 
     else null 
     end as parent, 
     null  as 'Root!1', 
     OrderID as 'Order!2!OrderID!element', 
     CustomerID as 'Order!2!CustomerID!element', 
     ItemID  as 'LineItem!3!ItemID!element', 
     ItemName as 'LineItem!3!ItemName!element' 
    from rsOrders 
group by grouping sets ((), (OrderID, CustomerID), (OrderID, CustomerID, ItemID, ItemName)) 
order by OrderID, CustomerID, ItemID, ItemName 
    for xml explicit, type