Re: left outer join only select newest record

Gary Stainburn, 23.05.2012 11:47:
> Here is a select to show the problem. There is one stock record and two tax
> records. What I'm looking for is how I can return only the second tax record,
> the one with the highest ud_id
>
> select s_stock_no, s_regno, s_vin, s_created, ud_id, ud_handover_date from
> stock s left outer join used_diary u on s.s_regno = u.ud_pex_registration
> where s_stock_no = 'UL15470';
>
> s_stock_no | s_regno | s_vin | s_created |
> ud_id | ud_handover_date
> ------------+---------+-------------------+----------------------------+-------+------------------
> UL15470 | YG12*** | KNADN312LC6****** | 2012-05-21 09:15:31.569471 |
> 41892 | 2012-04-06
> UL15470 | YG12*** | KNADN312LC6****** | 2012-05-21 09:15:31.569471 |
> 42363 | 2012-05-16
> (2 rows)
>

Something like:

select *
from (
select s_stock_no,
s_regno
s_vin,
s_created,
ud_id,
ud_handover_date,
row_number() over (partition by s_stock_no order by ud_id desc) as rn
from stock s
left outer join used_diary u on s.s_regno = u.ud_pex_registration
where s_stock_no = 'UL15470'
) t
where rn = 1

The "partition by s_stock_no order" isn't really necessary as your where clause already limits that to a single stock_no.
But in case you change that statement to return more than one stock_no in the future it will be necessary.