Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 16: A Brief XML Primer
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First, we need to alter the OrderID to have information on what element it belongs to:
SELECT CustomerID,
COUNT(*) AS ‘CustomerID/OrderCount’
FROM Sales.SalesOrderHeader Orders
WHERE CustomerID = 29890 OR CustomerID = 30067
GROUP BY CustomerID
FOR XML PATH;
By adding the “/”, and then placing CustomerID before the slash, we are telling SQL Server that
OrderCount is below CustomerID in a hierarchy. Now, there are many ways an XML hierarchy can be
structured, so let’s see what SQL Server does with this:
298908
3006712
Now, if you recall, we wanted to make OrderCount an attribute of CustomerID, so, while we have
OrderCount below CustomerID in the hierarchy, it’s still not quite in the place we wanted it. To do that,
we can combine / and @, but we need to fully define all the hierarchy. Now, since I suspect this is a bit
confusing, let’s take it in two steps — first, the way we might be tempted to do it, but that will yield a
similar error to the earlier example:
SELECT CustomerID,
COUNT(*) AS ‘CustomerID/@OrderCount’
FROM Sales.SalesOrderHeader Orders
WHERE CustomerID = 29890 OR CustomerID = 30067
GROUP BY CustomerID
FOR XML PATH;
Error time:
Msg 6852, Level 16, State 1, Line 1
Attribute-centric column ‘CustomerID/@OrderCount’ must not come after a
non-attribute-centric sibling in XML hierarchy in FOR XML PATH.
To fix this, we need to understand a bit about how things are constructed when building the XML tags.
The key is that the tags are essentially built in the order you list them. So, if you are wanting to add attributes
to an element, you need to keep in mind that they are part of the element tag — that means you need
to define any attributes before you define any other content of that element (sub elements or raw text).
In our case, we are presenting the CustomerID as being raw text, but the OrderCount as being an attribute
(OK, backwards of what would be likely in real life, but hang with me here). This means we are
telling SQL Server things backwards. By the time it sees the OrderCount information it is already done
with attributes for CustomerID and can’t go back.
So, to fix things for us, we simply need to tell it about the attributes before we tell it about any more elements
or raw text:
SELECT COUNT(*) AS ‘CustomerID/@OrderCount’,
CustomerID