SQL Server 2008 R2：使用存储为BLOB的XML（图像数据类型）

Question

A database on the MS SQL Server 2008 R2 has a column which is stored as a BLOB (has a "image" data type) . I also know that the BLOB contains XML.

Is there any way for reporting services to extract this information? How would I query or use the data that is stored within the XML BLOB?

I have read something along the line of casting the SQL IMAGE data type to the XML data type; then use @xml.query to get element/attribute values, would this be a good idea? How would I cast the BLOB (image data type) into XML data type? How do I check if my XML have a schema or not (hence typed or untyped XML)?

Or are there easier ways of retrieving data within the BLOB that contains XML to use it to generate a SSRS web report ?

Answer 1

Yes, you can cast the Image to Xml and then use features such as XQuery to parse the Xml document. You will however first need to cast it through VARBINARY as well.

SELECT CAST(cast(SomeXmlStoredAsBlob AS VARBINARY(MAX)) AS XML) AS MyXml
FROM MyTable

I would recommend changing the column type ASAP - if all data is Xml, then convert it to Xml as per above, and if there are different formats, then use VARBINARY(MAX)

SqlFiddle here

Answer 2

Yes, you can use SQL Server to extract data from your XML blob into a table.

You need to read in your blob value, then convert it into a variable of type xml , and from there, you can use some complicated syntax to query it.

Here's a little example:

DECLARE @str nvarchar(2000)

SET @str = ''
SET @str = @str + '<users>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Mike</firstName>'
SET @str = @str + '     <lastName>Gledhill</lastName>'
SET @str = @str + '     <age>31</age>'
SET @str = @str + '  </user>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Mark</firstName>'
SET @str = @str + '     <lastName>Stevens</lastName>'
SET @str = @str + '     <age>42</age>'
SET @str = @str + '  </user>'
SET @str = @str + '  <user>'
SET @str = @str + '     <firstName>Sarah</firstName>'
SET @str = @str + '     <lastName>Brown</lastName>'
SET @str = @str + '     <age>23</age>'
SET @str = @str + '  </user>'
SET @str = @str + '</users>'

DECLARE @xml xml
SELECT @xml = CAST(CAST(@str AS VARBINARY(MAX)) AS XML) 

--  Iterate through each of the "users\user" records in our XML
SELECT 
    x.Rec.query('./firstName').value('.', 'nvarchar(2000)') AS 'FirstName',
    x.Rec.query('./lastName').value('.', 'nvarchar(2000)') AS 'LastName',
    x.Rec.query('./age').value('.', 'int') AS 'Age'
FROM @xml.nodes('/users/user') as x(Rec)

This gives us these results:

Cool, hey ?

The downside is that this isn't particularly fast.

In my app, I use code like this, but write out the "table version" of this data into a regular SQL Server table.

You really don't want to be trying to do reporting based on directly loading and parsing XML blobs...