xml.exist - sql:column to sequence - sql

Question

I try to create a query with xml.exist by using the sql:column-function where the value of the column should be transformed into a usable XQuery-sequence.
This is the query with a static sequence, which is working.
SELECT
FieldA
, FieldB
FROM
MyTable
WHERE
FieldC.exist('DSAuth/role[#id=("195", "267", "350")')
To get a dynamic sequence i would use a table function with returns a table with a column "IDsequence" that have all id's as a string. e.g. ' "195", "267", "350" '.
The table function should return only one row! With multiple rows it works, but i have to group the result at last, which is bad for performance.
SELECT
FieldA
, FieldB
FROM
MyTable
CROSS APPLY
dbo.MyFunc(0) AS f
WHERE
FieldC.exist('DSAuth/role[#id=sql:column("f.IDsequence")]')
Is there a way to get a usable sequence for XQuery from sql:column("f.IDsequence")?
Thanks for help.
Edit:
The problem in performance is that FieldB (and a few more fields) is a xml column, so i have to convert it to group by.
SELECT
FieldA
, CAST(CAST(FieldB AS nvarchar(max)) AS xml) AS FieldB
FROM
MyTable
CROSS APPLY
dbo.MyFunc(0) AS f
WHERE
FieldC.exist('DSAuth/role[#id=sql:column("f.IDsequence")]')
GROUP BY
FieldA
, CAST(FieldB AS nvarchar(max))

Answer 1

I don't know if this is the easiest approach, but you might try to include your list into the XML and use it in the predicate like here:
--A mockup-table to show the principles
DECLARE #tbl TABLE(TheXml XML)
INSERT INTO #tbl VALUES
(
N'<root>
<a>1</a>
<a>2</a>
</root>'
)
,(
N'<root>
<a>1</a>
</root>'
)
,(
N'<root>
<a>3</a>
<a>4</a>
</root>'
);
--This is easy: Just one value
SELECT * FROM #tbl WHERE TheXml.exist('/root/a[. cast as xs:int?=1]')=1;
--This is your sequence.
--But you cannot introduce the value list with sql:column() or sql:variable().
SELECT * FROM #tbl WHERE TheXml.exist('/root/a[. cast as xs:int?=(2,3)]')=1;
--But you can add the values to your XML before like in this cte
DECLARE #values TABLE(val INT);
INSERT INTO #values VALUES(2),(3);
WITH cte(NewXml) AS
(
SELECT (SELECT (SELECT val AS [#val] FROM #values FOR XML PATH('values'),TYPE)
,TheXml AS [*]
FOR XML PATH(''),TYPE
)
FROM #tbl t
)
SELECT NewXml.query('/root') TheXml
FROM cte
WHERE NewXml.exist('/root/a[. cast as xs:int?=/values/#val]')=1;
The intermediate XML looks like this:
<values val="2" />
<values val="3" />
<root>
<a>1</a>
<a>2</a>
</root>
The final .query('/root') will return the previous XML unchanged.
UPDATE
The same would work with an introduction on string base like here:
WITH cte(NewXml) AS
(
SELECT (SELECT CAST(N'<values val="2" /><values val="3" />' AS XML)
,TheXml AS [*]
FOR XML PATH(''),TYPE
)
FROM #tbl t
)
SELECT NewXml.query('/root') TheXml
FROM cte
WHERE NewXml.exist('/root/a[. cast as xs:int?=/values/#val]')=1