Re: Arguments to foreign tables?

Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Tue, 2012-11-06 at 09:19 +0100, Ronan Dunklau wrote:
>> If you don't mind, do you have a specific use-case for this ?

> Let's say that your remote data source is a stream of data that is not
> actually being stored anywhere, e.g. network events. The data you want
> to retrieve are all events with a timestamp less than X, and you assume
> that the timestamp is monotonically increasing (so as soon as you get to
> X, the read is finished).

> An SRF isn't good enough because it always materializes (and that's the
> only way it allows you to control initialization and teardown of the
> stream connection). But you don't want to have to define a new foreign
> table each time. It would be better if there were a way to pass the
> argument X to the FDW mechanism.

That particular example can be handled perfectly well today, with

select * from stream_table where tscol < 'whatever';

The FDW could be coded to throw an error if the query doesn't provide a
WHERE clause that constrains the timestamp column suitably. It does
mean that you have to expose the "argument" as a result column, but at
least for this use-case that hardly seems like a problem.

regards, tom lane