Created with your sample data and you can query as below:
Select [Date], Client_id,
Stuff((Select ','+Item_desc from #alldata where [Date] = a.[Date] and [Client_id] = a.Client_id for xml path('')), 1,1,'')
from #alldata a
group by [Date], Client_id
Input table:
create table #alldata ([Date] date, Client_id int, Item_desc varchar(15))
insert into #alldata([date], Client_id, Item_desc) values
('2017-02-01', 12 ,'GLOVES')
,('2017-02-01', 12 ,'HAT')
,('2017-02-01', 12 ,'SHOES')
,('2017-02-01', 25 ,'GLOVES')
Output as below:
+------------+-----------+-----------------------------+
| Date | Client_id | Item_Desc |
+------------+-----------+-----------------------------+
| 2017-02-01 | 12 | GLOVES, HAT, SHOES |
| 2017-02-01 | 25 | GLOVES |
+------------+-----------+-----------------------------+