SQL Server XQuery返回错误

Question

I am performing a query against an XML data type column in SQL Server 2012. An example of the data is:

<ns:Resume xmlns:ns="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume">
  <ns:Name>
    <ns:Name.Prefix></ns:Name.Prefix>
    <ns:Name.First>Shai</ns:Name.First>
    <ns:Name.Middle></ns:Name.Middle>
    <ns:Name.Last>Bassli</ns:Name.Last>
    <ns:Name.Suffix></ns:Name.Suffix>
  </ns:Name>
  ...
</ns:Resume>

I am trying to write a query to return the first names.

This query returns a list of first names as expected:

WITH XMLNAMESPACES ('http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume' AS ns)
SELECT [Resume].query('(//ns:Name.First)').value('.[1]', 'nvarchar(100)')
FROM   HumanResources.JobCandidate;

However, this query returns an error:

WITH XMLNAMESPACES ('http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume' AS ns)
SELECT [Resume].value('(//ns:Name.First)[1]', 'nvarchar(100)')
FROM   HumanResources.JobCandidate;

Error:

Msg 9314, Level 16, State 1, Line 2
XQuery [HumanResources.JobCandidate.Resume.value()]: Cannot implicitly atomize or apply 'fn:data()' to complex content elements, found type 'xs:anyType' within inferred type '(element(ns{ http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume }:Name.First,xs:string) | element(ns{ http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume }:Name.First,xs:anyType)) ?'.

There's some basic understanding that I'm missing here but I'm not sure what it is. Can someone enlighten me? Why does the second query return an error?

Answer 1

Your XPath expression could lead to multiple rows being returned, for each row in the SQL Server table. You'll need to use a CROSS APPLY and a call to .nodes() to get that information you're after:

WITH XMLNAMESPACES ('http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume' AS ns)
SELECT 
    JobCandidateID,
    ResNames.value('(ns:Name.First)[1]', 'nvarchar(100)')
FROM   
    HumanResources.JobCandidate
CROSS APPLY
    [Resume].nodes('/ns:Resume/ns:Name') AS XTbl(ResNames)

That should return all JobCandidateID values and all first names defined in the Resume XML column for each row in the table.

If you can be sure that there's only ever going to be a single <name> tag in your XML column, then you could also shorten this to:

WITH XMLNAMESPACES ('http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/Resume' AS ns)
SELECT 
    JobCandidateID,
    [Resume].value('(/ns:Resume/ns:Name/ns:Name.First)[1]', 'nvarchar(100)')
FROM   
    HumanResources.JobCandidate