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

Notice that our order count remained a text element of the row — only the column that we identified as
an attribute moved in. We could take this to the next step by naming our count and prefixing it to make
it an attribute also:
SELECT CustomerID AS '@CustomerID',
COUNT(*) AS '@OrderCount'
FROM Sales.SalesOrderHeader Orders
WHERE CustomerID = 29890 OR CustomerID = 30067
GROUP BY CustomerID
FOR XML PATH;
With this, we no longer have our loose text for the element:
Also notice that SQL Server was smart enough to realize that everything was contained in attributes —
with no lower level elements or simple text, it chose to make it a self-closing tag (see the “/” at the end
of the element).
So, why did I indicate that this stuff was tricky? Well, there are a lot of different “it only works if . . .”
kind of rules here. To demonstrate this, let’s make a simple modification to our original query. This one
seems like it should work, but SQL Server will throw a hissy fit if you try to run it:
SELECT CustomerID,
COUNT(*) AS ‘@OrderCount’
FROM Sales.SalesOrderHeader Orders
WHERE CustomerID = 29890 OR CustomerID = 30067
GROUP BY CustomerID
FOR XML PATH;
What I’ve done here is to go back to CustomerID as its own element. What, at first glance, you would
expect to happen is to get a CustomerID element with OrderCount as an attribute, but it doesn’t quite
work that way:
Msg 6852, Level 16, State 1, Line 1
Attribute-centric column '@OrderCount' must not come after a non-attribute-centric
sibling in XML hierarchy in FOR XML PATH.
The short rendition of the “What’s wrong?” answer is that it doesn’t really know what it’s supposed to
be an attribute of. Is it an attribute of the row, or an attribute of the CustomerID?
Yes, a forward slash.
Chapter 16: A Brief XML Primer
Much like @, this special character indicates special things you want done. Essentially, you use it to
define something of a path — a hierarchy that relates an element to those things that belong to it. It can
exist anywhere in the column name except as the first character. To demonstrate this, we’re going to utilize
our last (failed) example, and build into it what we were looking for when we got the error.
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