SQL query xml data from varchar(max) column - sql-server

Question

I have a table called Content which has a varchar(max) column called data.
The data in this column is in XML format, and I want to query an attribute in the XML.
Below is the top couple of lines of the XML, it is the p3:manifestId I want to query so my output would basically be Some_Data (I've obviously desensitized this).
Is this possible?
<manifest xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p3="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.w3.org/2001/XMLSchema-instance"
p3:manifestDateTime="2016-02-17T17:34:29.5925096Z"
p3:manifestVersion="1.1" p3:manifestId="Some_Data">
<p3:productList>
<p3:product p3:releaseDateTime="2016-02-17T17:34:29.5925096Z" p3:installSeqId="2" p3:uninstallSeqId="2" p3:releaseNum="1" p3:productType="doc" p3:productId="WEDREZ020RRRP0GGG001" p3:mfgCode="GIRE">

Answer 1

The only thing which might be complicated here, are the namespaces. How is this XML generated? It is quite unusual to see the same namespace (http://www.w3.org/2001/XMLSchema-instance) as default and with two different aliases...
DECLARE #mockup TABLE(ID INT IDENTITY, YourXML VARCHAR(MAX));
INSERT INTO #mockup VALUES
('<manifest xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p3="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.w3.org/2001/XMLSchema-instance"
p3:manifestDateTime="2016-02-17T17:34:29.5925096Z"
p3:manifestVersion="1.1" p3:manifestId="Some_Data">
<!--Some more stuff-->
</manifest>');
--This approach does not look at namespaces at all. I use the wildcard *:
SELECT CAST(YourXML AS XML).value(N'(/*:manifest/#*:manifestId)[1]',N'nvarchar(max)')
FROM #mockup;
--This approach declares all needed namespaces in advance (best approach in most cases):
WITH XMLNAMESPACES(DEFAULT 'http://www.w3.org/2001/XMLSchema-instance'
,'http://www.w3.org/2001/XMLSchema-instance' AS p3)
SELECT CAST(YourXML AS XML).value(N'(/manifest/#p3:manifestId)[1]',N'nvarchar(max)')
FROM #mockup;
--This approach is usefull, if you really do not need more than one value. I use one alias ns1 for all different occurances of this namespace:
SELECT CAST(YourXML AS XML).value(N'declare namespace ns1="http://www.w3.org/2001/XMLSchema-instance";
(/ns1:manifest/#ns1:manifestId)[1]',N'nvarchar(max)')
FROM #mockup;