XQuery [value()] issue for Dynamic SQL variable in Select Stateemt - sql

Question

I'm try to make the code below dynamic as there can be different names for the 'name' attribute in the page 'node'.
When I run the code below it returns the error 'XQuery [value()]: 'value()' requires a singleton (or empty sequence), found operand of type 'xdt:untypedAtomic *''
I feel my main issue is in the line
'C.value('(/level1/level2/template/page/#name)[sql:variable("#Counter")]','NVARCHAR(MAX)') AS [Page Name]'
where I am trying to make '#counter' variable dynamic.
Does anyone have any solutions please?
XML FOR ID 9371
<level1>
<level2>
<template width="594" height="500">
<page Cid="1" name="Test Page Name" colour="-3355393">
<image Cid="8" x="432" y="8" w="148" h="95" KeyImage="32861" Ratio="y" />
<formattedText Cid="14" x="9" y="22" w="253" h="38">
<p>
<p>
Text
</p>
</p>
</formattedText>
</page>
<page Cid="6" name="Properties">
<formattedText Cid="7" x="200" y="148" w="208" h="228">
<p>
<p>
<t>Created by </t>
<t b="b">Joe Bloggs</t>
</p>
<p />
<p>
<t>Date published 30/05/2017</t>
</p>
</formattedText>
</page>
</template>
</level2>
</level1>
RESULTS FROM SQL Query
** Present Result
Page Name | Demographics
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Test Page Name | <page Cid="1" name="Test Page Name" colour="-3355393"><image Cid="8" x="432" y="8" w="148" h="95" KeyImage="32861" Ratio="y" /><formattedText Cid="14" x="9" y="22" w="253" h="38"><p><p>Text</p></p> </formattedText></page>
Test Page Name | <page><formattedText Cid="7" x="200" y="148" w="208" h="228"><p><p> <t>Created by </t><t b="b">Joe Bloggs</t></p><p /><p><t>Date published 30/05/2017</t> </p></formattedText></page>
** Desired Result
Page Name | Demographics
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Test Page Name | <page Cid="1" name="Test Page Name" colour="-3355393"><image Cid="8" x="432" y="8" w="148" h="95" KeyImage="32861" Ratio="y" /><formattedText Cid="14" x="9" y="22" w="253" h="38"><p><p>Text</p></p> </formattedText></page>
Properties | <page><formattedText Cid="7" x="200" y="148" w="208" h="228"><p><p> <t>Created by </t><t b="b">Joe Bloggs</t></p><p /><p><t>Date published 30/05/2017</t> </p></formattedText></page>
DECLARE #TableName VARCHAR(40),
#opxml AS XML,
#hDoc AS INT,
#SQL NVARCHAR (MAX)
SELECT #opxml =
a.[filedata]
FROM [database].[dbo].[xmlfile2] a
where [Id] = 9371
DECLARE #Counter INT
DECLARE #MaxNo INT
SET #Counter=1
SET #MaxNo=(SELECT
COUNT(CAST('<page>' + CAST(C.query('./child::node()') as nvarchar(max)) + '</page>' as xml))
FROM #opxml.nodes('/level1/level2/template/page') AS T(C))
WHILE ( #Counter <= #MaxNo)
BEGIN
SELECT
C.value('(/level1/level2/template/page/#name)[sql:variable("#Counter")]','NVARCHAR(MAX)') AS
[Page Name],
CAST('<page>' + CAST(C.query('./child::node()') as nvarchar(max)) + '</page>' as xml) AS [Page_XML]
, ROW_NUMBER() OVER (ORDER BY t.c)
FROM #opxml.nodes('/level1/level2/template/page') AS T(C)
SET #Counter = #Counter + 1
END

Answer 1

I think
SELECT
C.value('#name','NVARCHAR(MAX)') AS [Page Name],
C.query('<page>{node()}</page>') AS [Page_XML],
ROW_NUMBER() OVER (ORDER BY t.c)
FROM #opxml.nodes('/level1/level2/template/page') AS T(C)
might suffice to produce the wanted result without the need for a WHILE loop.
I think the original problem with the long path inside of value() (e.g. C.value('(/level1/level2/template/page/#name)[sql:variable("#Counter")]','NVARCHAR(MAX)')) is due to the static type checking of XQuery in SQL server and to avoid it you basically need to add another predicate that ensures the type checker knows a single value is returned e.g. C.value('(/level1/level2/template/page/#name)[sql:variable("#Counter")][1]','NVARCHAR(MAX)')
For me, the code
DECLARE #opxml AS XML
SET #opxml = N'<level1>
<level2>
<template width="594" height="500">
<page Cid="1" name="Test Page Name" colour="-3355393">
<image Cid="8" x="432" y="8" w="148" h="95" KeyImage="32861" Ratio="y" />
<formattedText Cid="14" x="9" y="22" w="253" h="38">
<p>
<p>
Text
</p>
</p>
</formattedText>
</page>
<page Cid="6" name="Properties">
<formattedText Cid="7" x="200" y="148" w="208" h="228">
<p>
<p>
<t>Created by </t>
<t b="b">Joe Bloggs</t>
</p>
<p />
<p>
<t>Date published 30/05/2017</t>
</p>
</p>
</formattedText>
</page>
</template>
</level2>
</level1>'
SELECT
C.value('#name','NVARCHAR(MAX)') AS [Page Name],
C.query('<page>{node()}</page>') AS [Page_XML],
ROW_NUMBER() OVER (ORDER BY t.c)
FROM #opxml.nodes('/level1/level2/template/page') AS T(C)
produces the table
Page Name Page_XML (Kein Spaltenname)
Test Page Name <page><image Cid="8" x="432" y="8" w="148" h="95" KeyImage="32861" Ratio="y" /><formattedText Cid="14" x="9" y="22" w="253" h="38"><p><p>
Text
</p></p></formattedText></page> 1
Properties <page><formattedText Cid="7" x="200" y="148" w="208" h="228"><p><p><t>Created by </t><t b="b">Joe Bloggs</t></p><p /><p><t>Date published 30/05/2017</t></p></p></formattedText></page> 2
so at least the Page_Name seems to be easily populated by using e.g. C.value('#name','NVARCHAR(MAX)') AS [Page Name]