TSQL: Return elements of a group as XML

Question

I try to aggregate values per group into one XML. I am on SQL Server 2016.

My raw-data looks like this (here strictly stiped down to the problem. My real values are not generic.):

create table #data (group_id int, value1 char(10), value2 char(10), value3 char(10));

insert #data values 
(1,'a1', 'b1', 'c1'),
(1,'a2', 'b2', 'c2'),
(1,'a3', 'b3', 'c3'),
(2,'a4', 'b4', 'c4');

I am looking for an aggregate function that would return one XML (per group)

select 
  group_id,
  **my_XML_aggregation** as [XML-values]
from #data
group by group_id

The expected result XML for the first group (group_id = 1) should look like (names of the elements are not relevant to the problem)

<group>
   <row>
     <value1>a1<value1>
     <value2>b1<value1>
     <value3>c1<value1>
  </row>
   <row>
     <value1>a2<value1>
     <value2>b2<value1>
     <value3>c2<value1>
  </row>
   <row>
     <value1>a3<value1>
     <value2>b3<value1>
     <value3>c3<value1>
  </row>
</group>

I know how to aggregate a pattern-separated string. This would not do the job. Even to put the pattern-aggregated string into one XML element is no alternative. I am looking for the structured information within the XML.

Answer 1

Try like this:

drop table if exists #data ;

create table #data (group_id int, value1 varchar(10), value2 varchar(10), value3 varchar(10));

insert #data values 
(1,'a1', 'b1', 'c1'),
(1,'a2', 'b2', 'c2'),
(1,'a3', 'b3', 'c3'),
(2,'a4', 'b4', 'c4');

with groups as
(
  select distinct group_id from #data 
)
select group_id,
       (
         select value1, value2, value3
         from #data
         where group_id = groups.group_id
         for xml path, root('group'), type
       ) group_doc
from groups 

outputs

group_id    group_doc
----------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1           <group><row><value1>a1</value1><value2>b1</value2><value3>c1</value3></row><row><value1>a2</value1><value2>b2</value2><value3>c2</value3></row><row><value1>a3</value1><value2>b3</value2><value3>c3</value3></row></group>
2           <group><row><value1>a4</value1><value2>b4</value2><value3>c4</value3></row></group>