HQL - Concatenate Column Values from Multiple Rows into a Single Column having duplicate id

I want to concatenate the duplicate id to single row.

 user.id | group.name        
    1    |     a
    1    |     b
    1    |     c

I want it like :-

user.id | group.name        
   1    |   a,b,c

All I want it in hql. How do I write in hql query where User left join Group. Need Help!!!