Re: NEXT VALUE FOR <sequence>

On 3 October 2014 00:18, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thomas Munro <munro(at)ip9(dot)org> writes:
>> I suppose one approach would be to use command
>> IDs as the scope.
>
> The spec clearly says one value per row, not one per statement; so
> command ID is very definitely not the right thing.

I think (command ID, estate->es_processed) would work. Tracking those
two values in SeqTableData would allow you to detect the level change
meaning the next tuple has been returned by a SELECT, updated by an
UPDATE or inserted by an INSERT. This could be activated by a new
2-argument nextval with a boolean argument to request the standard
behaviour. Then NEXT VALUE FOR could be translated to nextval(...,
true).

But I just can't figure out how to get my hands on the current EState
or QueryDesc from inside a fmgr function, so I can't reach
estate->es_processed from nextval...

Best regards,
Thomas Munro