Based on your sample data: -
IF object_id('tempdb..#yourTable') IS NOT NULL
BEGIN
DROP TABLE #yourTable;
END;
SELECT id, CAST(ItemId AS XML) AS ItemId
INTO #yourTable
FROM (VALUES(1, '<itemids><itemid>259</itemid><itemid>489</itemid></itemids>'),
(2, '<itemids><itemid>6834262</itemid><itemid>489</itemid></itemids>'),
(3, '<itemids><itemid>6603537</itemid></itemids>')
)a(id, ItemId);
You'd do it like this: -
SELECT id, ParamValues.ItemId.value('.','INT') AS ItemId
FROM #yourTable
OUTER APPLY ItemId.nodes('/itemids/itemid') ParamValues(ItemId);