How to retrieve rows with XML column that have specific child node? - sql-server

Question

I have a table in SQL Server with an XML column:
CREATE TABLE dbo.XmlData (
id INT IDENTITY,
data XML
);
The XML stored in the data column is dynamic, I mean, only some of them have certain child node. Additionally, this nodes appear in different locations within the XML structure.
Example 1, /RootNode/FindMe:
<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>Two</ChildNodeTwo>
<ChildNodeThree>Three</ChildNodeThree>
<FindMe>FindMe</FindMe>
</RootNode>
Example 2, /RootNode/ChildNodeThree/Deeper/FindMe and /RootNode/ChildNodeTwo/FindMe :
<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>
<FindMe>FindMe</FindMe>
</ChildNodeTwo>
<ChildNodeThree>
<Deeper>
<FindMe>FindMe</FindMe>
</Deeper>
</ChildNodeThree>
</RootNode>
There are rows with the XML column that doesn't have the <FindMe/> node.
I need to write a query to retrieve only the rows that have the <FindMe/> node. No matter its location within the XML structure.

Answer 1

The first thing to know is, that //FindMe will trigger a deep search. That means: Find this node whereever it exists in the XML. A single / marks the root element (Start the search at the beginning) and no slash at all marks the current node (Continue from the context node):
In the following there are some examples how one could query for a node name:
A dummy table for tests:
CREATE TABLE dbo.DummyTbl (
id INT IDENTITY,
Remark VARCHAR(100),
data XML
);
INSERT INTO DummyTbl VALUES
('FindMe is on second level',
'<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>Two</ChildNodeTwo>
<ChildNodeThree>Three</ChildNodeThree>
<FindMe>FindMe 1</FindMe>
</RootNode>')
,('FindMe is two times somewhere deeper',
'<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>
<FindMe>FindMe 2a</FindMe>
</ChildNodeTwo>
<ChildNodeThree>
<Deeper>
<FindMe>FindMe 2b</FindMe>
</Deeper>
</ChildNodeThree>
</RootNode>')
,('FindMe does not exist',
'<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>
</ChildNodeTwo>
<ChildNodeThree>
<Deeper>
<FindMeNot>Something else</FindMeNot>
</Deeper>
</ChildNodeThree>
</RootNode>')
,('FindMe exists, but is empty',
'<RootNode>
<ChildNodeOne>One</ChildNodeOne>
<ChildNodeTwo>
</ChildNodeTwo>
<ChildNodeThree>
<Deeper>
<FindMe/>
</Deeper>
</ChildNodeThree>
</RootNode>');
Different queries:
--All FindMe nodes (inlcuding the empty one)
SELECT d.id,d.Remark
,f.value('.','nvarchar(max)') FindMeNode
FROM dbo.DummyTbl AS d
CROSS APPLY d.data.nodes('//FindMe') AS A(f)
--All IDs where there is at least one "FindMe"-node
SELECT d.id,d.Remark
FROM dbo.DummyTbl AS d
WHERE d.data.exist('//FindMe')=1
GO
--All IDs where there is at least one "FindMe"-node, but not the empty one
SELECT d.id,d.Remark
FROM dbo.DummyTbl AS d
WHERE d.data.exist('//FindMe/text()')=1
--Find IDs, where there is at least one empty FindMe node
SELECT d.id,d.Remark
FROM dbo.DummyTbl AS d
WHERE d.data.exist('//FindMe[empty(text())]')=1
--Now with a variable name to search for
DECLARE #SearchForName NVARCHAR(100)='FindMe';
SELECT d.id,d.Remark
FROM dbo.DummyTbl AS d
WHERE d.data.exist('//*[local-name()=sql:variable("#SearchForName")]/text()')=1
GO
--Clean up
DROP TABLE dbo.DummyTbl;