在SQL Server中为空时，生成表结构的XML

Question

I am trying to generate a table containing one row that contains the XML of each temporary table in a stored procedure.

The problem is when the table is empty the FOR XML PATH('RS'), root('OR_RS') returns null .

What I want is: when the table is empty, return the structure of this table something like this :

<OR_RS>
    <ContactCode></ContactCode>
    <EmailPaper></EmailPaper>
    <ShortEmail></ShortEmail>
    <WebSite></WebSite>
    <Providers></Providers>
</OR_RS>  

I have tried to do this :

-- ,ISNULL( (SELECT  * FROM #OR_RS FOR XML PATH('RS'), root('OR_RS')), (SELECT ISNULL(ContactCode,'')  , ISNULL(EmailPaper,'') , ISNULL(ShortEmail,'') , ISNULL(WebSite,'')  , ISNULL(Providers,'')  FROM #OR_RS FOR XML RAW)) as OR_RS

but it returns always Null :

 SELECT 1 as Id, (SELECT  * FROM #OR_MK   FOR XML PATH('MK'), root('OR_MK') ) as OR_MK
,(SELECT  * FROM #OR_CA FOR XML PATH('CA'), root('OR_CA') ) as OR_CA 
-- ,ISNULL( (SELECT  * FROM #OR_RS FOR XML PATH('RS'), root('OR_RS')), (SELECT ISNULL(ContactCode,'')  , ISNULL(EmailPaper,'') , ISNULL(ShortEmail,'') , ISNULL(WebSite,'')  , ISNULL(Providers,'')  FROM #OR_RS FOR XML AUTO)) as OR_RS
,(SELECT * FROM #OR_RS FOR XML PATH('RS'), root('OR_RS')) as OR_RS
,(SELECT  * FROM #OR_DC FOR XML PATH('DC'), root('OR_DC') ) as OR_DC
,(SELECT  * FROM #BENEFICIARY FOR XML PATH('BEN'), root('BENEFICIARY') ) as BENEFICIARY
,(SELECT * FROM #MK_REPORT for XML PATH('REP'), root('MK_REPORT')) as MK_REPORT

Answer 1

Whatever you try to do with this...

You might want to have a look at sp_describe_first_result_set , but, since this is a procedure, it will not be that easy to get its result into your query...

You can use a trick (a RIGHT JOIN ) to enforce a resultset. And with ELEMENTS XSINIL you force the engine to include the column in any case. Otherwise XML takes missing elements as NULL , so your empty result would not be written into the result XML at all otherwise. Try this:

DECLARE @tbl TABLE(ID INT IDENTITY,SomeValue INT,SomeString VARCHAR(100));

SELECT * 
FROM @tbl
RIGHT JOIN (SELECT 1 AS x) AS tbl ON 1=1
FOR XML RAW, ELEMENTS XSINIL

The result

<row xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <ID xsi:nil="true" />
  <SomeValue xsi:nil="true" />
  <SomeString xsi:nil="true" />
  <x>1</x>
</row>

If you want to get more details, you might add ,XMLDATA or ,XMLSCHEMA to generate full meta data.