It seems to me that the only thing a primary key constraint gives me that I don't get from a unique key is support for replication. A unique key can ibe the traget of a foreign key constraint, it can include nullable columns, it can be supported by a clustered or a non-clustered index. So if I don't want replication, why should I create an extra column which is in prcatise meaningless to act as primary key?

Here's some code that does nothing useful except sho that unique keys work quite happily:

use tempdb

create table target (

a int unique clustered

)

insert target

select 1 union all

select null

create table pointer (

a int references target(a) on delete cascade,

b int,

c int,

constraint uq_pointer unique clustered (a,b,c)

)

insert pointer

select 1,2,3 union all

select 1,2,null union all

select 1,null,3 union all

select null,2,3 union all

select null,null,3 union all

select null,2,null union all

select 1,null,null union all

select null,null,null

select * from pointer -- returns 8 rows

insert pointer select null,null,null -- this statement fails demonstrating that a

-- unique constraint requires only absence of equality,

-- not presence of inequality

drop table pointer, target

I don't understand why you would want the table to have a very short half-life either. As far as I can see, it's perfectly OK if the table has a very long half-life - in fact it may as well last for ever. If its rows have a very short half life that might be interesting - I have seen some cases where a table is not worth replicating for standby since the time required to reach a decision to cut over to the standby system and do it is high enough that the replicated data in that table would be worthless - the table itself would still be needed because new items would appear in it and be dealt with (quickly).