SQL WHERE clause with multiple XML attributes - sql

Question

I have table in database with XML column. Now I need to select some rows by two attributes from XML.
So far I've come up with this:
SELECT o.Id
FROM Objects o
WHERE o.SerializedObject.value('(/object/param[#id="111"]/#value)[1]', 'varchar(8)') = '-1'
AND o.SerializedObject.value('(/object/param[#id="222"]/#value)[1]', 'varchar(8)') = '8'
EDIT:
XML is like:
<object>
<param id="1" value="111"/>
<param id="2" value="222"/>
...
<param id="200" value="4545"/>
<object>
Each object has ~2k params.
I'm wondering if there is a better way to do that with single XML query.

Answer 1

This depends on your XML (you did not show an example, but I assume this is kind of EAV).
You can try using XML's method .exist():
DECLARE #mockup TABLE(ID INT IDENTITY,Comment VARCHAR(100),SerializedObject XML);
INSERT INTO #mockup VALUES
('just one of them','<object><param id="111" value="-1"/></object>')
,('both, but wrong values','<object><param id="111" value="-1"/><param id="222" value="-1"/></object>')
,('both, should fit','<object><param id="111" value="-1"/><param id="222" value="8"/></object>')
SELECT o.Id,o.Comment,o.SerializedObject
FROM #mockup o
WHERE o.SerializedObject.exist('/object[param[#id="111" and #value="-1"] and param[#id="222" and #value="8"]]')=1;
.exist() is the fastest here, because it does not return any value. It will just return 1 on the first occurance found. This is especially fast, when there are many occurances of a <param id="111" value="???"> Otherwise you'd have to shred the whole lot and place the filter on the whole resultset.
And - of course! - the necessary hint: As told in a comment by Jeroen Mostert dealing with bigger XMLs might turn out as a bottle neck. If you need this more often, you might think about a relational design instead of big XMLs...