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

The downside to using AUTO is that the resulting XML data model ends up being slightly more complex.
The upside is that the data is more explicitly broken up into a hierarchical model. This makes life easier
when the elements are more significant breaking points — such as where you have a doubly sorted
report (for example, Order sorted within Customer).
EXPLICIT
The word “explicit” is an interesting choice for this option — it loosely describes the kind of language
you’re likely to use while trying to create your query. The EXPLICIT option takes much more effort to
prepare, but it also rewards that effort with very fine granularity of control over what’s an element and
what’s an attribute, as well as what elements are nested in what other elements. EXPLICIT enables you
to define each level of the hierarchy and how each level is going to look. In order to define the hierarchy,
you create what is internally called the universal table. The universal table is, in many respects, just like
any other result set you might produce in SQL Server. It is usually produced by making use of UNION
statements to piece it together one level at a time, but you could, for example, build much of the data in
a UDF and then make a SELECT against that to produce the final XML. The big difference between the
universal table and a more traditional result set is that you must provide sufficient metadata right within
your result set such that SQL Server can then transform that result set into an XML document in the
schema you desire.
What do I mean by “sufficient metadata”? Well, to give you an idea of just how complex this can be, let’s
look at a real universal table:
Tag Parent Customer!1!
CustomerID
Customer!1!
CompanyName
1 NULL ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
2 1 ALFKI Alfreds
Futterkiste
Chapter 16: A Brief XML Primer
Order!2!
OrderID
NULL NULL
Order!2!OrderDate
10643 1997-08-25
00:00:00.000
10692 1997-10-03
00:00:00.000
10702 1997-10-13
00:00:00.000
10835 1998-01-15
00:00:00.000
10952 1998-03-16
00:00:00.000
11011 1998-04-09
00:00:00.000
11078 1999-05-01
00:00:00.000
Continued
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