Horton

Re: Changed SRF in targetlist handling

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Merlin Moncure <mmoncure@gmail.com>, David Fetter <david@fetter.org>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2016-06-06T16:41:38Z
Lists: pgsql-hackers 
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> If the SRFs return a different number of rows the LCM behavior kicks in and
> you get Robert's second result.

Only if the periods of the SRFs are relatively prime.  That is, neither of
his examples demonstrate the full weirdness of the current behavior; for
that, you need periods that are multiples of each other.  For instance:

SELECT generate_series(1, 2), generate_series(1, 4); 
 generate_series | generate_series 
-----------------+-----------------
               1 |               1
               2 |               2
               1 |               3
               2 |               4
(4 rows)

That doesn't comport with any behavior available from LATERAL.

			regards, tom lane

Commits

  1. Remove obsoleted code relating to targetlist SRF evaluation.

  2. Doc: improve documentation of new SRF-in-tlist behavior.

  3. Move targetlist SRF handling from expression evaluation to new executor node.

  4. Don't split up SRFs when choosing to postpone SELECT output expressions.