为FOR XML EXPLICIT UNION结果分配给一个变量

Question

此查询工作正常

SELECT 1 AS TAG, NULL AS parent, 1 [dog!1] 
UNION (SELECT 1,NULL, 3) 
FOR XML EXPLICIT, ROOT('dogs') 

我想将它分配给一个变量。这不工会工作正常：

DECLARE @x xml 
SET @x = ((
    (SELECT 1 AS TAG, NULL AS parent, 1 [dog!1] 
    FOR XML EXPLICIT, ROOT('dogs')) 
)) 

只要我介绍了工会这是行不通的：

DECLARE @x xml 
SET @x = ((
    (SELECT 1 AS TAG, NULL AS parent, 1 [dog!1] 
    UNION (SELECT 1,NULL, 3) 
    FOR XML EXPLICIT, ROOT('dogs')) 
    )) 

尝试过各种各样的事情。我缺少

Answer 1

你只需要添加更多的子查询级是这样的：

DECLARE @X XML = 
(
    SELECT * FROM 
    (
    SELECT 1 AS TAG, NULL AS parent, 1 [dog!1] 
    UNION 
    SELECT 1,NULL, 3 
)X 
    FOR XML EXPLICIT, ROOT('dogs') 
); 

SELECT @X;