Re: Endgame for all those SELECT FOR UPDATE changes: fix plan node order

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Oct 26, 2009 at 10:30 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> One problem with this is that there isn't any good way for someone to
>> get back the old behavior if they want to. Which might be a perfectly
>> reasonable thing, eg if they know that no concurrent update is supposed
>> to change the sort-key column. The obvious thing would be to allow
>>
>> select * from (select * from foo order by col limit 10) ss for update;
>>
>> to apply the FOR UPDATE last. Unfortunately, that's not how it works
>> now because the FOR UPDATE will get pushed down into the subquery.

> Could the desired behavior be obtained using a CTE?

Nope, we push FOR UPDATE into WITHs too. I don't really see any way to
deal with this without some sort of semantic changes.

regards, tom lane