update script

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declare @case table(id int,condition varchar(2),scondition varchar(2),rn int)
insert into @case values(1,'HF','AA',1)
insert into @case values(1,'CA','LL',1)
insert into @case values(1,'XY','LL',1)
--insert into @case select id,condition,scondition,row_number() over (partition by id,intensity order by id) as rn from [CASE]
update @case set condition = (case
                                                                when condition in ('HF','CA') then scondition
                                                                when condition not in ('HF','CA') then null 
                                                         end)
select * from @case

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Regards, RSingh