SQL Server - join rows into comma separated list - sql-server

Question

Let's suppose I have a temporary table which looks like this:
+----+------+
| Id | Value|
+----+------+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 2 |
+----+------+
And I want my table to be like this:
+----+----------+
| Id | ValueList|
+----+----------+
| 1 | 1,2,3 |
| 2 | 1,2 |
+----+----------+
So basically I need to group my values as a comma separated list.
I already tried the following:
SELECT Id, STUFF((SELECT ',' + CAST(VALUE AS varchar) FROM #MyTable FOR XML PATH('')), 1 ,1, '') AS ValueList
FROM #MyTable
GROUP BY Id
But I get something like:
+----+---------------------+
| Id | ValueList |
+----+---------------------+
| 1 | 1,1,1,1,1,1,... |
+----+---------------------+
I cant find what I am doing wrong. Could someone help with this query? Or point me to a right direction?
Thank you.

Answer 1

You are missing the condition inside the sub query.
SELECT t2.Id, STUFF((SELECT ',' + CAST(VALUE AS varchar) FROM #MyTable t1 where t1.Id =t2.ID FOR XML PATH('')), 1 ,1, '') AS ValueList
FROM #MyTable t2
GROUP BY t2.Id
Demo

Answer 2

One alternative to using GROUP BY on the Id would be to use select distinct:
SELECT DISTINCT
Id,
STUFF((SELECT ',' + CAST(t2.VALUE AS varchar)
FROM #MyTable t2
WHERE t2.Id = t1.Id
FOR XML PATH('')), 1 ,1, '') AS ValueList
FROM #MyTable t1
Demo

Answer 3

One can also combine a FOR XML with a CROSS APPLY (or an OUTER APPLY) for this.
Example snippet:
declare #T table (id int, value int);
insert into #T values (1,1),(1,2),(1,3),(2,1),(2,2);
select id, stuff(x.list,1,1,'') as list
from (select distinct id from #T) as t
cross apply (
select concat(',',t2.value)
from #T t2
where t2.id = t.id
for xml path('')
) x(list)
order by id;
Result:
id list
-- -----
1 1,2,3
2 1,2
And starting from MS Sql Server 2017, STRING_AGG can be used instead.
select id, string_agg(value,',') as list
from Yourtable t
group by id;

Answer 4

Try this :
create table #t(id int, value int)
insert into #t values
(1,1),
(1,2),
(1,3),
(2,1),
(2,2)
SELECT t2.Id,
STUFF((SELECT ',' + CAST(VALUE AS varchar) FROM #t t1 where t1.Id =t2.ID FOR XML PATH('')), 1 ,1, '') AS list
FROM #t t2
GROUP BY t2.Id
output :
Id list
--- -------
1 1,2,3
2 1,2

Answer 5

Simple Solution
SELECT Id, GROUP_CONCAT(Value) as ValueList FROM MyTable GROUP BY Id;
add distinct to values if required
SELECT Id, GROUP_CONCAT(DISTINCT Value) as ValueList FROM MyTable GROUP BY Id;