need to update Class value if Name occurs ONLY one time with Class value class1

Question

I have data like below,

create table #tbl (Name varchar(20), Class varchar(20))  
insert into #tbl values ('A', 'class1'), ('A', 'class2'), ('B', 'class1'), ('C', 'class2'), ('D', 'class3'), ('D', 'class1'), ('E', 'class4')  
select * from #tbl  
drop table #tbl  

• A has 2 items
• B has 1 item with class1
• C has 1 item with class2
• D has 2 items
• E has one item with class4

I need to update class of "B" with value "XX" which has 1 items with class1, rest I need to ignore.

Expected output should be,

Answer 1

;With cte As
(Select Name, Class, Count(*) Over(Partition By Name) As Cnt
From #tbl)
Update cte
Set Class = 'XX'
Where Class = 'class1' And Cnt = 1;

Tom