Re: Strange result with LATERAL query

Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> Something is wrong with the way chgParam is being handled in Agg nodes.
> The code in ExecReScanAgg seems to assume that if the lefttree doesn't
> have any parameter changes then it suffices to re-project the data from
> the existing hashtable; but of course this is nonsense if the parameter
> is in an input to an aggregate function.

It looks like it's sufficient to do this:

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 1ec2515..f468fad 100644
*** a/src/backend/executor/nodeAgg.c
--- b/src/backend/executor/nodeAgg.c
*************** ExecReScanAgg(AggState *node)
*** 3425,3435 ****
return;

/*
! * If we do have the hash table and the subplan does not have any
! * parameter changes, then we can just rescan the existing hash table;
! * no need to build it again.
*/
! if (outerPlan->chgParam == NULL)
{
ResetTupleHashIterator(node->hashtable, &node->hashiter);
return;
--- 3425,3436 ----
return;

/*
! * If we do have the hash table and there are no relevant parameter
! * changes, then we can just rescan the existing hash table; no need
! * to build it again.
*/
! if (node->ss.ps.chgParam == NULL &&
! outerPlan->chgParam == NULL)
{
ResetTupleHashIterator(node->hashtable, &node->hashiter);
return;

I'm not sure if it's worth trying to distinguish whether the Param is
inside any aggregate calls or not. The existing code gets the right
answer for

select array(select x+sum(y) from generate_series(1,3) y group by y)
from generate_series(1,3) x;

and we'd be losing some efficiency for cases like that if we fix
it as above. But is it worth the trouble?

regards, tom lane