TSQL How to concatenate column from joined table with group by - sql-server

Question

I have 2 connected tables: Producto and Productos_ProductosRelacionados
Producto Productos_ProductosRelacionados
|id|referencia| |id|idProducto|idProductoRelacionado|
|1 | A | |1 | 1 | 2 |
|2 | B | |2 | 1 | 3 |
|3 | C | |3 | 3 | 4 |
|4 | D | |4 | 3 | 5 |
|5 | E |
I need this:
|idProducto|referencia|
| 1 | B,C |
| 2 | |
| 3 | D,E |
I have older SQL server so can not use STRING_AGG.
So far I only achieve concatenating idProductoRelacionado:
|idProducto|idProductoRelacionado|
| 1 | 2,3 |
with:
SELECT pr1.idProducto
,STUFF((
SELECT ',' + CONVERT(varchar, pr.idProductoRelacionado)
FROM [Productos_ProductosRelacionados] as pr
WHERE pr.idProducto = pr1.idProducto
FOR XML PATH('')), 1, 1, '') as RelacionadosID
FROM [dbo].[Producto] as p1
join [Productos_ProductosRelacionados] as pr1 on p1.id = pr1.idProductoRelacionado
GROUP BY pr1.idProducto
If I try the same approach to concatenate referencia column it gives me: "Column 'dbo.Producto.id' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause."
select pr1.idProducto
,STUFF((
SELECT ',' + p.referencia
FROM [dbo].[Producto] as p
WHERE p.id = p1.id
FOR XML PATH('')), 1, 1, '') as RelacionadosREF
from [dbo].[Producto] as p1
join [Productos_ProductosRelacionados] as pr1 on p1.id = pr1.idProductoRelacionado
GROUP BY pr1.idProducto
I do not understand the difference between 2 queries, why first one is working and second is not.

Answer 1

Simple Join should work. Check SQLFiddle
SELECT
id,
(SELECT
cast (p1.referencia as varchar(100)) + ','
FROM producto p
LEFT JOIN Productos_ProductosRelacionados pr
on pr.idProduct = p.id
LEFT JOIN producto p1
on p1.id = pr.idProductoRelacionado
WHERE p.id = src.id
FOR XML PATH('')) as referencia
FROM
producto src;

Answer 2

I ran into this a while back. You have to add a join to your stuff statement:
create table #prod (
id int,
ref varchar(1)
)
insert into #prod values
(1,'A'),
(2,'B'),
(3,'C'),
(4,'D'),
(5,'E')
create table #prod_rel (
id int,
pid int,
id_rel int
)
insert into #prod_rel values
(1,1,2),
(2,1,3),
(3,3,4),
(4,3,5)
select distinct
pid
,STUFF(
(SELECT ',' + c.ref FROM #prod_rel b inner join #prod c on c.id = b.id_rel where b.pid = a.pid FOR XML PATH ('')), 1, 1, ''
)
from #prod_rel a
drop table #prod
,#prod_rel

Answer 3

You can use recursive query method, like this:
--Create tables for example
select * into #Producto from (
select 1 id,'A' referential union all select 2,'B' union all select 3,'C' union all select 4,'D' union all select 5,'E'
) tmp;
select * into #Productos_ProductosRelacionados from (
select 1 id,1 idProducto,2 idProductoRelacionado union all select 2,1,3 union all select 3,3,4 union all select 4,3,5
) tmp;
-- Recurse query
With tmp as (
select ROW_NUMBER() over(partition by f1.ID order by f1.id, f3.referential desc) RangID,
count(*) over(partition by f1.ID order by f1.id) NbID,
f1.id, f3.referential
from #Producto f1
left outer join #Productos_ProductosRelacionados f2 on f1.id=f2.idProducto
left outer join #Producto f3 on f2.idProductoRelacionado=f3.id
),
Recurse as (
select f1.id, f1.RangID, f1.NbID, cast(f1.referential as varchar(2000)) referential, 1 rangrecur from tmp f1 where RangID=1
union all
select f1.id, f1.RangID, f1.NbID, cast(isnull(f1.referential, '') + ',' + isnull(f2.referential, '') as varchar(2000)) referential, f2.rangrecur + 1 as rangrecur
from tmp f1 inner join Recurse f2 on f1.id=f2.id and f1.RangID-1=f2.RangID
)
select ID, Referential from recurse
where NbID=rangrecur
order by ID;