XML query() works, value() requires singleton found xdt:untypedAtomic

Question

I have a typed xml document stored as text. So I use CONVERT the data type to xml by using a Common Table Expression in order to be able to use XML methods:

Answer 1

For those interested in performance I ran a query to compare these approaches and the first option with "() and add a [1]" was MUCH faster than ".query('strFranchise').value('.',...)".

Difference in Execution plan was 15% to 85% when running one after the other on same data. So ()[1] is over 5 times faster! Execution plan is much different.

Answer 2

I believe this might also do:

SELECT 
   x.requestpayload.query('declare namespace s="http://blah.ca/api";
                           /s:validate-student-request/s:student-id').value('.', 'int') 
  as studentid
FROM xoutput x

Answer 3

You need to use this:

SELECT 
        x.requestpayload.value('declare namespace s="http://blah.ca/api";
            (/s:validate-student-request/s:student-id)[1]', 'int') 
    AS
        studentid
    FROM 
        xoutput x

You need to put your XPath in ( ... ) and add a [1] to simply select the first value of that sequence.