Question

这可能很简单，但我在这个上面有一个脑屁......

我正在使用FOR XML EXPLICIT作为子查询的一部分，以便我可以显式定义返回的XML的格式。因此我使用UNION ALL来定义该格式。

这工作正常，但如果该子查询中没有行，我需要它返回NULL ...此时它返回一个空的根元素：<codes/>。那是因为我需要定义的第一行。

Here is a sqlfiddlecom with everything below for you to look at.

这是目前的TSQL版本......

SELECT
    P.[PROJECTID],
    P.[PROJECTNAME],
    (   SELECT *
        FROM (
                SELECT
                    1 AS TAG,
                    NULL AS PARENT,
                    NULL AS 'codes!1',
                    NULL AS 'code!2!!element',
                    NULL AS 'code!2!split'
                UNION ALL
                SELECT
                    2 AS TAG,
                    1 AS PARENT,
                    NULL,                   
                    C.[CODE],
                    C.[SPLIT]
                FROM [CODES] C
                WHERE C.[PROJECTID] = P.[PROJECTID]
             ) AS [CODEXMLDATA]
        FOR XML EXPLICIT
    ) AS [CODESXML]
FROM [PROJECTS] P

示例数据将与

一致

PROJECTS table
PROJECTID PROJECTNAME
1         This
2         That
3         Other

CODES table
PROJECTID CODE SPLIT
1         ABC  45
1         BCD  65
2         CDE  100

结果是......

PROJECTID PROJECTNAME CODESXML
1         This        <codes><code split="45">ABC</code><code split="55">BCD</code></codes>
2         That        <codes><code split="100">CDE</code></codes>
3         Other       <codes/>

我需要的结果是（注意第3行的NULL）......

PROJECTID PROJECTNAME CODESXML
1         This        <codes><code split="45">ABC</code><code split="55">BCD</code></codes>
2         That        <codes><code split="100">CDE</code></codes>
3         Other       NULL

当没有NULL时，有人可以告诉我如何让它返回CODES吗？

Answer 1

试试此代码

SELECT distinct 
    P.[PROJECTID],
    P.[PROJECTNAME],
    case when (p.projectid = c.projectid) then 
    (   SELECT *
        FROM (
                SELECT
                    1 AS TAG,
                    NULL AS PARENT,
                    NULL AS 'codes!1',
                    NULL AS 'code!2!!element',
                    NULL AS 'code!2!split'
                UNION ALL
                SELECT
                    2 AS TAG,
                    1 AS PARENT,
                    NULL,                   
                    C.[CODE],
                    C.[SPLIT]
                FROM [CODES] C
                WHERE C.[PROJECTID] = P.[PROJECTID]
             ) AS [CODEXMLDATA]
        FOR XML EXPLICIT
    ) else null end AS [CODESXML]
FROM [PROJECTS] P
left join [CODES] C on  C.[PROJECTID] = P.[PROJECTID]

SQLFiddle：http://sqlfiddle.com/#!3/f8788/7/0

从没有行的XML EXPLICIT子查询返回NULL

1 个答案: