Group By String Agg, Sql Server

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--Sql Server 2014 Express Edition
--Batches are separated by 'go'

--select @@version as 'sql server version'

create table session_table
(
    
    sessionId varchar(100),
    log_timestamp varchar(100)
)
    
    
insert into session_table values('1','27-10-2017');
insert into session_table values('1','28-10-2017');
insert into session_table values('2','27-10-2017');
insert into session_table values('2','28-10-2017');
insert into session_table values('3','27-10-2017');
insert into session_table values('4','29-10-2017');
insert into session_table values('4','27-10-2017');
insert into session_table values('3','29-10-2017');
insert into session_table values('5','28-10-2017');
insert into session_table values('5','10-10-2017');
insert into session_table values('8','23-10-2017');
insert into session_table values('8','29-10-2017');

select a.sessionId, stuff( ( select ',' , b.log_timestamp from session_table b 
                     where a.sessionId = b.sessionId 
                     order by b.log_timestamp for xml path('a'), type).value('.','nvarchar(max)'),1,1,'') as time
from session_table a
group by a.sessionId

View schema
Execution time: 0,03 sec, rows selected: 6, rows affected: 12, absolute service time: 0,19 sec