Это то, что вы хотите?
select
id,
[user_id],
datestamp,
f.i.value('itemKey[1]', 'varchar(50)') as itemKey,
f.i.value('itemValue[1]', 'varchar(50)') as itemValue
from YourTable as T
cross apply T.formdata.nodes('/formfields/item') as f(i)
Тест:
declare @T table
(
id int,
user_id int,
datestamp datetime,
formdata xml
)
insert into @T (id, user_id, datestamp, formdata)
values (1, 1, getdate(),
'<formfields>
<item>
<itemKey>USER_NAME</itemKey>
<itemValue>test</itemValue>
</item>
<item>
<itemKey>value2</itemKey>
<itemValue>test</itemValue>
</item>
<item>
<itemKey>MYID</itemKey>
<itemValue>5468512</itemValue>
</item>
<item>
<itemKey>testcheckbox</itemKey>
<itemValue>item1,item3</itemValue>
</item>
<item>
<itemKey>samplevalue</itemKey>
<itemValue>item3</itemValue>
</item>
<item>
<itemKey>accept_terms</itemKey>
<itemValue>True</itemValue>
</item>
</formfields>
'
)
select
id,
[user_id],
datestamp,
f.i.value('itemKey[1]', 'varchar(50)') as itemKey,
f.i.value('itemValue[1]', 'varchar(50)') as itemValue
from @T as T
cross apply T.formdata.nodes('/formfields/item') as f(i)
Результат:
id user_id datestamp itemKey itemValue
1 1 2011-05-23 15:38:55.673 USER_NAME test
1 1 2011-05-23 15:38:55.673 value2 test
1 1 2011-05-23 15:38:55.673 MYID 5468512
1 1 2011-05-23 15:38:55.673 testcheckbox item1,item3
1 1 2011-05-23 15:38:55.673 samplevalue item3
1 1 2011-05-23 15:38:55.673 accept_terms True