Re: [PATCHES] 8.2 features? - Mailing list pgsql-hackers

Joe Conway <mail@joeconway.com> writes:
> Tom Lane wrote:
>> I think the place we'd ultimately like to get to involves changing the
>> executor's Result node type to have a list of targetlists and sequence
>> through those lists to produce its results

> I was actually just looking at that and ended up thinking that it might 
> be better to deal with it one level down in ExecProject (because it is 
> already passing targetlists directly to ExecTargetList).

I'd vote against that, because (a) ExecProject is used by all executor
node types, and we shouldn't add overhead to all of them for the benefit
of one; (b) ExecProject doesn't actually have any internal state at the
moment.  To keep track of which targetlist to evaluate next, it would
not only need some internal state, it would have to be told the current
"es_direction".  This stuff fits much better at the exec node level ---
again, I'd suggest looking at Append for a comparison.

But really the executor part of this is not the hard part; what we need
to think about first is what's the impact on the Query datastructure
that the parser/rewriter/planner use.

I'm still liking the idea of pushing multi-values into a jointree node
type.  Basically this would suggest representing "VALUES ..." as if it
were "SELECT * FROM VALUES ..." (which I believe is actually legal
syntax per spec) --- in the general case you'd need to have a Query node
that has a trivial "col1, col2, col3, ..." targetlist and then the
multiple values lists are in some kind of jointree entry.  But possibly
this could be short-circuited somehow, at least for INSERT.

BTW, I noticed an interesting property of historical Postgres behavior:
you can put a table reference into a VALUES targetlist.

regression=# create table foo (like tenk1);
CREATE TABLE
regression=# insert into foo values (tenk1.*);
ERROR:  missing FROM-clause entry for table "tenk1"
LINE 1: insert into foo values (tenk1.*);                               ^
regression=# set add_missing_from to 1;
SET
regression=# insert into foo values (tenk1.*);
NOTICE:  adding missing FROM-clause entry for table "tenk1"
LINE 1: insert into foo values (tenk1.*);                               ^
INSERT 0 10000
regression=# 

So that last is really exactly equivalent to
insert into foo select * from tenk1;

I do not feel a need to support this sort of thing when there are
multiple VALUES targetlists, but it'd be nice not to break it for the
single-targetlist case.  At least not till we're ready to disable
add_missing_from entirely.
        regards, tom lane