將動態構建的'for xml'語句插入到表或變量中

Question

我有一種情況，我試圖從臨時表中將未填充字段的列表轉換爲逗號分隔語句。

所以給出的示例中的數據（這將始終是單個行，並可能在一個臨時表（作爲實際數據將來自源表的多個））：

Field1  Field2 Field3 Field4 
'aaa'  null  ''  null 

和映射的

FieldName Question Section 
'Field1'  'Q1'  'Sec1' 
'Field2'  'Q2'  'Sec1' 
'Field3'  'Q3'  'Sec2' 
'Field4'  'Q4'  'Sec2' 

表，我想以下結果：

Section UnansweredQs 
'Sec1' 'Q2' 
'Sec2' 'Q3, Q4' 

我得儘可能的逗號做分隔的問題清單：

create table #testData (f1 varchar(50), f2 int, f3 varchar(50), f4 varchar(50)) 
create table #qlist (fieldName varchar(5), question varchar(3), section varchar(5)) 

insert into #qlist values ('f1', 'q1', 'sec1'), ('f2', 'q2', 'sec1'), ('f3', 'q3', 'sec2'), ('f4', 'q4', 'sec2') 

insert into #testData values ('asda', null, '', null) 

然後

declare @usql nvarchar(max) = '' 
declare @sql nvarchar(max) 
declare @xml xml 

--build a gargantuan set of union statements, comparing the column value to null/'' and putting q# if it is 
set @usql = 
    (
    select 'select case when ' + c.name + ' is null or ' + c.Name + ' = '''' then ''' + q.question + ', '' else '''' end from #testData union ' 
    from tempdb..syscolumns c 
    inner join #qlist q 
     on c.name = q.fieldName 
    where c.id = object_id('tempdb..#testData') 
    for xml path('') 
    ); 
--remove the last 'union', append for xml path to pivot the rows into a single column of concatenated rows 
set @usql = left(@usql, len(@usql) - 6) + ' for xml path('''')' 

print @usql 

--remove final comma 
--get the position of the last comma in the select statment (ie after the final unanswered question) 
declare @lastComma int = charindex(',', reverse(@usql)) 
--add the bit before the last comma, and the bit after the last comma but skip the actual comma :) 
set @usql = left(@usql, len(@usql) - @lastComma) + right(@usql, @lastComma - 2) 

exec (@usql) 

有了這個，我得到

XML_F52E2B61-18A1-11d1-B105-00805F49916B 
---------------------------------------- 
q2, q3, q4 

但我不能得到那個結果集到另一個表或變量（通過insert into #tmpresult exec (@usql)方法）。

通常與Msg 1086, Level 15, State 1, Line 1 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.錯誤。

我試過各種東西，包裝，取消工會，CTE的，但不能得到它的工作。

Answer 1

我有一個查詢爲您：

with cte as (
    select 
     N.Name 
    from Table1 
     cross apply (values 
      ('Field1', Field1), 
      ('Field2', Field2), 
      ('Field3', Field3), 
      ('Field4', Field4) 
     ) as N(Name,Value) 
    where N.Value is null or N.Value = '' 
) 
select distinct 
    T2.Section, 
    stuff(
     (
      select ', ' + TT.Question 
      from Table2 as TT 
       inner join cte as c on c.Name = TT.FieldName 
      where TT.Section = T2.Section 
      for xml path(''), type 
     ).value('.', 'nvarchar(max)') 
    , 1, 2, '') as UnansweredQs 
from Table2 as T2 

你可以自己把它變成動態:)

sql fiddle demo

Answer 2

沒有必要使用動態SQL來做到這一點。

declare @X xml 

set @X = (
     select * 
     from #testData 
     for xml path('root'), elements xsinil, type 
     ) 

select section, 
     (
     select ', '+Q2.question 
     from #qlist as Q2 
     where Q1.section = Q2.section and 
      @X.exist('/root/*[local-name() = sql:column("Q2.fieldName")][. = ""]') = 1 
     for xml path(''), type 
     ).value('substring(text()[1], 2)', 'varchar(max)') as UnansweredQs 
from #qlist as Q1 
group by Q1.section 

SQL Fiddle