Re: COPY FROM WHEN condition

On Oct 11, 2018, at 10:35 AM, David Fetter <david@fetter.org> wrote:
> 
>> It didn't get far, but you may want to take a look at a rejected patch for
>> copy_srf() (set returning function)
>> https://www.postgresql.org/message-id/CADkLM%3DdoeiWQX4AGtDNG4PsWfSXz3ai7kY%3DPZm3sUhsUeev9Bg%40mail.gmail.com
>> https://commitfest.postgresql.org/12/869/
>> 
>> Having a set returning function gives you the full expressiveness of SQL,
>> at the cost of an extra materialization step.
> 
> I wonder whether something JIT-like could elide this. A very
> interesting subset of such WHEN clauses could be pretty
> straight-forward to implement in a pretty efficient way.

Are you thinking something like having a COPY command that provides results in such a way that they could be referenced
ina FROM clause (perhaps a COPY that defines a cursor…)?