create table t1 (id int, name varchar(128))
create table t2 (id int,t1_id int, val1 varchar(128),val2 varchar(128))


insert into t1 values (1, 'a'),(2,'b'),(3,'c')
insert into t2 values (1,1,'aa','bb'),(2,1,'cc','dd'),(3, 2,'cf','sad'),(4,2,'asd','dasd')


select t1.id, t1.name,dad
from t1
cross apply
(select t2.val1+',' as [text()] from t2 where t2.t1_id = t1.id for xml path('')) D (dad)