Question

我的SQL查询出了一些问题，创建了一个XML文件。我想UNION这个查询，但它不起作用。

(SELECT 1 AS "ns0:kindOfItem",
code AS "ns0:wholeCode",
REPLACE(weight, ',', '.') AS "ns0:weight",
1 AS "ns0:ammountOfNumbers",
(SELECT price AS "ns0:value",
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:sendedItems'), TYPE),
(SELECT 
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:present'), TYPE)
FROM [PL].[dbo].[dk_documents] where id in (1,2,3)
FOR XML PATH('test'))

这个查询工作正常，但是当我尝试UNION时，就像这里一样：

(SELECT 1 AS "ns0:kindOfItem",
code AS "ns0:wholeCode",
REPLACE(weight, ',', '.') AS "ns0:weight",
1 AS "ns0:ammountOfNumbers",
(SELECT price AS "ns0:value",
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:sendedItems'), TYPE),
(SELECT 
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:present'), TYPE)
FROM [PL].[dbo].[dk_documents] where id in (1,2,3)

UNION

(SELECT 1 AS "ns0:kindOfItem",
code AS "ns0:wholeCode",
REPLACE(weight, ',', '.') AS "ns0:weight",
1 AS "ns0:ammountOfNumbers",
(SELECT price AS "ns0:value",
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:sendedItems'), TYPE),
(SELECT 
'EUR' as "ns0:currency"
FOR XML PATH ('ns0:present'), TYPE)
FROM [PL2].[dbo].[dk_documents] where id in (1,2,3)
FOR XML PATH('test'))

此查询给我一个错误：

数据类型xml不能用作UNION，INTERSECT的操作数或EXCEPT运营商，因为它不具有可比性。

Answer 1

使用UNION将删除结果的重复值，因此SQL Server必须将第一部分的XML与第二部分进行比较，并确定它们是否相等且未针对XML实现。

您可能不希望重复检查，因此更改为UNION ALL，它也适用于XML数据。

Answer 2

您可能对此感兴趣：

请比较以下

单词＆＃34; test＆＃34;发生在两个列表中。 UNION将隐式执行DISTINCT，因此＆＃34;测试＆＃34;只出现一次。

SELECT * 
FROM (VALUES('this'),('is'),('a'),('test')) AS tbl(Words)
UNION
SELECT * 
FROM (VALUES('and'),('another'),('test')) AS tbl(Words);

与UNION ALL相同会让＆＃34;测试＆＃34;出现两次

SELECT * 
FROM (VALUES('this'),('is'),('a'),('test')) AS tbl(Words)
UNION ALL
SELECT * 
FROM (VALUES('and'),('another'),('test')) AS tbl(Words);

您可以将UNION SELECT放入周围的SELECT（UNION或UNION ALL，并为整个结果集设置FOR XML PATH

命名空间是重复创建的，没有错，但很烦人（请参阅：https://stackoverflow.com/a/35648751/5089204和链接的Connect-Article）

WITH XMLNAMESPACES(DEFAULT 'Dummy') 
SELECT *
FROM
(
    SELECT * 
    FROM (VALUES('this'),('is'),('a'),('test')) AS tbl(Words)
    UNION
    SELECT * 
    FROM (VALUES('and'),('another'),('test')) AS tbl(Words)
) AS MetaTable
FOR XML Path(''),ROOT('UNION_TEST');

这将返回两个列表，每个列表都在自己的XML标记中，也重复命名空间（参见前面）

WITH XMLNAMESPACES(DEFAULT 'Dummy') 
SELECT
 (
    SELECT * 
    FROM (VALUES('this'),('is'),('a'),('test')) AS tbl(Words)
    FOR XML PATH(''),ROOT('FirstBlock'),TYPE
 )
,(
    SELECT * 
    FROM (VALUES('and'),('another'),('test')) AS tbl(Words)
    FOR XML PATH(''),ROOT('FirstBlock'),TYPE
 )
FOR XML Path(''),ROOT('UNION_TEST');

最后你也可以使用它（使用ALL或不使用）：

WITH XMLNAMESPACES(DEFAULT 'Dummy') 
SELECT * 
FROM (VALUES('this'),('is'),('a'),('test')) AS tbl(Words)
UNION ALL
SELECT * 
FROM (VALUES('and'),('another'),('test')) AS tbl(Words)
FOR XML PATH(''),ROOT('UNION_TEST');

在创建XML文件时在SQL中联合

2 个答案: