檢視、內嵌函數、衍生資料表及子查詢中若包含集合運算子，則 FOR XML 子句無效。若要解決此問題，請使用衍生資料表語法包裝內含集合運算子的 SELECT，並在其最上層套用 FOR XML。

The FOR XML clause is invalid in views, inline functions, derived tables, and subqueries when they contain a set operator. To work around, wrap the SELECT containing a set operator using derived table syntax and apply FOR XML on top of it.