union - SQL query to find the friends in a table -

i have 2 tables, users , friends. tables like:

users |  id   |  name   |  |  1    |  sam    |  |  2    |  harry  |          |  3    |  vivi   | |  4    | sabrina |  friends | uid   | friendid|  |  1    |    2    |     |  2    |    3    |   |  4    |    1    |  |  5    |    4    |  |  1    |    3    |   

i need find names of friends sam. tried doing same using union in sql query, couldn't desired output. can possibly required output doing same?

declare @answer nvarchar(max)='{' select @answer=@answer+u1.name+',' users u inner join friends f on f.uid=u.id inner join users u1 on u1.id=f.friendid u.id=<what ever want> //1 or 2 or 3 or 4  set @answer=substring(@answer,0,len(@answer)-1)+'}' select @answer