Re: Need LIMIT and ORDER BY for UPDATE

D. Dante Lorenso wrote:

> I'd really like to have ORDER BY and LIMIT for UPDATE and DELETE
> commands. Is this possible?
>
> UPDATE invoice i
> SET reserve_ts = NOW() + '1 hour'::timestamp
> FROM account a
> WHERE a.acct_id = i.acct_id
> AND i.reserve_ts < NOW()
> AND a.status = 'A'
> AND i.is_paid IS FALSE
> ORDER BY i.create_ts ASC
> LIMIT 1
> RETURNING invoice_id;
>
> This query would find JUST ONE invoice record which is not paid and
> reserve the right to operate on the row using the 'reserve_ts'
> column for all active accounts. The one row would be the oldest
> invoice matching the criteria. Only that one row would be updated
> and the invoice_id of the updated row (if any) would be returned.

> Can something like what I want be added in a future version? Ideas
> or alternatives? I don't see how I can rewrite this query as a
> single statement any other way and get the same expectations.

Doesn't this do it, assuming invoice_id is unique?

UPDATE invoice
SET reserve_ts = NOW() + '1 hour'::timestamp
where invoice_id =
(select invoice_id from invoice i,
account a
WHERE a.acct_id = i.acct_id
AND i.reserve_ts < NOW()
AND a.status = 'A'
AND i.is_paid IS FALSE
ORDER BY i.create_ts ASC
LIMIT 1)
RETURNING invoice_id;

- John Burger
MITRE