From: | Thomas Munro <munro(at)ip9(dot)org> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: NEXT VALUE FOR <sequence> |
Date: | 2014-10-04 21:45:21 |
Message-ID: | CADLWmXXPuwhrLNVw0J-CRdPJtSz7sd-0j8tsD1PLod9bp21=Aw@mail.gmail.com |
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Lists: | pgsql-hackers |
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
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