--> 测试数据: @T
--创建个自定义函数
create function fn_insertsign(@str varchar(100))
returns varchar(100)
as
begin
    declare @i INT,@j int 
    select @i=ceiling(len(@str)/5.00), @j=0
    declare @s varchar(100) set @s=''
    while (@j<@i)
    begin
        set @s=@s+substring(@str,@j*5+1,5)+','
        set @j=@j+1
    end
    return @s
end

--测试数据
declare @T table (字段1 int,字段2 varchar(100))
insert into @T
select 1,'fkdsaewewjkeljelwjelwkejewlkew' union all
select 2,'ddsadsadadsadsadqwqwqewqeqwe'

--更新数据
update @T set 字段2=dbo.fn_insertsign(字段2)

select * from @T
/*
字段1         字段2
----------- ----------------------------------------
1           fkdsa,ewewj,kelje,lwjel,wkeje,wlkew,
2           ddsad,sadad,sadsa,dqwqw,qewqe,qwe,
*/