declare @id nvarchar(10)
set @id='a'
declare @Tb table
(
tmp nvarchar(400)
)
insert into @tb values('c,b,c,d,a')
update @tb set
tmp=
(case when charindex(@id,tmp)=1 then replace(tmp,@id+',','')
when charindex(@id,tmp)=(len(tmp)-len(@id)+1) then replace(tmp,','+@id,'')
else replace(tmp,','+@id+',',',')
end
)
select * from @tb