Re: [BUGS] Status of issue 4593

On Mon, Jan 12, 2009 at 8:32 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> I can see two ways forward:
>
>> 1) We document bluntly that ORDER BY + FOR UPDATE can return unordered
>> results, or
>
>> 2) We prohibit ORDER BY + FOR UPDATE, like we do with a number of other
>> clauses. (There would be no loss of functionality, because you can run
>> the query a second time in the transaction with ORDER BY.)
>
> That code has been working like this for eight or ten years now and this
> is the first complaint, so taking away functionality on the grounds that
> someone might happen to update the ordering column doesn't seem like the
> answer to me.

If the only case where ORDER BY + FOR UPDATE are not strictly
compatible is when the columns being updated are the same as the
columns of the sort, a blanket prohibition against using the two
together seems like it prohibits an awful lot of useful things someone
might want to do. Saying that you can run the query a second time as
a workaround so there's no loss of functionality is true only if you
accept the proposition that performance is not a requirement.

...Robert