Flattening hierarchical XML in SQL using the nodes() method

Question

I have a Stored Procedure that takes an XML document as a parameter similar in a structure to the following:

Answer 1

I seem to have answered my own question after a bit more looking around online:

SELECT
    grandparent.gname.value('@name', 'VARCHAR(15)'),
    parent.pname.value('@name', 'VARCHAR(15)'),
    child.cname.value('@name', 'VARCHAR(15)')
FROM
    @xmlFamilyTree.nodes('/grandparent') AS grandparent(gname)
CROSS APPLY
    grandparent.gname.nodes('*') AS parent(pname)
CROSS APPLY
    parent.pname.nodes('children/*') AS child(cname)

Using CROSS APPLY I can select the top-level grandparent node and use this to select the child parent nodes and so on. Using this method I have taken my query from executing in around 1 minute 30 seconds down to around 6 seconds.

Interestingly though, if I use the "old" OPEN XML method to retrieve the same data, the query executes in 1 second!

It seems like you may have to approach the use of these two techniques on a case-by-case basis depending on the expected size/complexity of the document being passed in.