SQL Server 2022

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create table yourtable (country varchar(100), value varchar(100));
insert into yourtable values ('FR',NULL);
insert into yourtable values ('FR',1);
insert into yourtable values ('FR',3);
insert into yourtable values ('MA',5);
insert into yourtable values ('MA',NULL);
insert into yourtable values ('MA',4);
insert into yourtable values ('ES',9);
insert into yourtable values ('ES',10);
insert into yourtable values ('ES',NULL);
9 rows affected

SELECT country, value FROM yourtable;


country
value


FR
null

FR
1

FR
3

MA
5

MA
null

MA
4

ES
9

ES
10

ES
null


SELECT country, STRING_AGG(COALESCE(value,'NULL'),',') AS value
FROM yourtable
GROUP BY country
ORDER BY country;


country
value


ES
9,10,NULL

FR
NULL,1,3

MA
5,NULL,4

country	value
FR	null
FR	1
FR	3
MA	5
MA	null
MA	4
ES	9
ES	10
ES	null