SQL Server - Replace text in XML variable based on join - sql

Question

For my situation, I have similar XML to the following:
DECLARE #MyXML XML
SET #MyXML =
'
<Students>
<Student>
<Nickname>Cat</Nickname>
<Name>Catherine</Name>
</Student>
<Student>
<Nickname>Cat</Nickname>
<Name>Joseph</Name>
</Student>
</Students>
'
SELECT T.Students.value('Nickname[1]', 'varchar(20)')
FROM #MyXML.nodes('/Students/Student[Nickname = "Cat"]') T(Students)
JOIN dbo.MyStudents CLASS ON T.Students.value('Name[1]', 'varchar(20)') = CLASS.StudentName
I want to update the records that get returned from this SELECT statement, replacing the Nickname with CLEARED. So, if dbo.MyStudents has Joseph but not Catherine, the resulting #MyXML variable would be:
<Students>
<Student>
<Nickname>Cat</Nickname>
<Name>Catherine</Name>
</Student>
<Student>
<Nickname>CLEARED</Nickname>
<Name>Joseph</Name>
</Student>
</Students>
Is there a way to do this by modifying the XML variable directly? Or will I need to put the XML variable into a temp table and perform a .modify on the temp table?
So far, examples that I have found do not have the conditional update with .modify based on the join.

Answer 1

Give this example a try. For more info see Syntax of the FOR XML Clause.
-- sample #MyStudents table
declare #MyStudents table (StudentName varchar(90), NickName varchar(90));
insert #MyStudents values('Kent', '');
insert #MyStudents values('Robert', 'Bobby');
insert #MyStudents values('Lisa', 'LB');
insert #MyStudents values('Venkat', 'Big Cat');
insert #MyStudents values('Catherine', 'Cat');
insert #MyStudents values('Joseph', 'Joey');
DECLARE #MyXML XML
SET #MyXML =
'<Students>
<Student>
<Nickname>Cat</Nickname>
<Name>Catherine</Name>
</Student>
<Student>
<Nickname>Joey</Nickname>
<Name>Joseph</Name>
</Student>
<Student>
<Nickname>Bonzo</Nickname>
<Name>Clifford</Name>
</Student>
</Students>'
select #MyXML = (
select (
select * from (
-- set existing #MyStudent records to CLEARED
select
'CLEARED' as NickName,
T.Students.value('Name[1]', 'varchar(20)') as Name
from #MyXML.nodes('/Students/Student') T(Students)
join #MyStudents CLASS ON T.Students.value('Name[1]', 'varchar(20)') = CLASS.StudentName
union
-- get students that aren't in #MyStudents table
select
T.Students.value('Nickname[1]', 'varchar(20)') as NickName,
T.Students.value('Name[1]', 'varchar(20)') as Name
from #MyXML.nodes('/Students/Student') T(Students)
where not exists(select 1 from #MyStudents s where s.StudentName = T.Students.value('Name[1]', 'varchar(20)'))
) as t1
for xml path('Student'), type)
for xml path('Students'), type)