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

FOR XML provides three different initial options for how you want your XML formatted in the results:
❑ RAW: This sends each row of data in your result set back as a single data element, with the element
name of “row” and with each column listed as an attribute of the “row” element. Even if
you join multiple tables, RAW outputs the results with the same number of elements as you
would have rows in a standard SQL query.
❑ AUTO: This option labels each element with the table name or alias that represents the source of
the data. If there is data output from more than one table in the query, the data from each table
is split into separate, nested elements. If AUTO is used, then an additional option, ELEMENTS, is
also supported if you would like column data presented as elements rather than as attributes.
❑ EXPLICIT: This one is certainly the most complex to format your query with, but the end result
is that you have a high degree of control of what the XML looks like in the end. With this option,
you impose something of a hierarchy for the data that’s being returned, and then format your
query such that each piece of data belongs to a specific hierarchy level (and gets assigned a tag
accordingly) as desired. This choice has largely been supplanted by the PATH option, and is here
primarily for backward compatibility.
❑ PATH: This was added to try and provide the level of flexibility of EXPLICIT in a more usable
format — this is generally going to be what you want to use when you need a high degree of
control of the format of the output.
Note that none of these options provide the required root element. If you want the XML document to be
considered to be well formed, then you will need to wrap the results with proper opening and closing
tags for your root element or have SQL Server do it for you (using the ROOT option described later).
While this is in some ways a hassle, it is also a benefit — it means that you can build more complex
XML by stringing multiple XML queries together and wrapping the different results into one XML file.
In addition to the four major formatting options, there are other optional parameters that further modify
the output that SQL Server provides in an XML query:
❑ XMLDATA/XMLSCHEMA: These tell SQL Server that you would like to prepend one of two forms of
an XML schema to the results. XMLDATA works under the older XDR format, which was common
before the W3C finalized the spec for XML schema documents. You’ll want to use
XMLSCHEMA here unless you have a very specific reason for using the older XDR format, as the
XMLDATA option is provided only for backward compatibility and does not support newer data
types added in SQL Server 2005 and 2008.
❑ ELEMENTS: This option is available only when you are using the AUTO formatting option. It tells SQL
Server that you want the columns in your data returned as nested elements rather than as attributes.
❑ BINARY BASE64: This tells SQL Server to encode any binary columns (binary, varbinary, image)
in base64 format. This option is implied (SQL Server will use it even if you don’t state it) if you
are also using the AUTO option. It is required when using EXPLICIT and RAW queries.
❑ TYPE: Tells SQL Server to return the results reporting the XML data type instead of the default
Unicode character type.
❑ ROOT: This option will have SQL Server add the root node for you so you don’t have to. You can
either supply a name for your root or use the default (root).
Let’s explore all these options in a little more detail.
Chapter 16: A Brief XML Primer
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