Thanks Tom,
that made it clear I made a mistake.
> That's the way it's supposed to be --- the scantuple slot is for
> scanning your subplan's output.
Browsing through the code I get the impression, that
- ecxt_scantuple is only used by Scan nodes (i.e. SeqScan, IndexScan, SubqueryScan and FunctionScan)
- ecxt_innertuple and ecxt_outertuple are used by Join nodes (but they don't use the ecxt_scantuple at all).
Is it right that the ecxt_scantuple is only used by leafnodes (Scans) and never by Joins?
> > I have written a new executor node Foo, with corresponding ExecFoo and
> make_foo functions. I have also written a new Expr type called Bar, along
> with a ExecEvalBar.
>
> > In make_foo I append some Bar columns. When I try to evaluate the Bar
> columns in ExecFoo via ExecProject, I need the Bar columns to access each
> other.
>
> That makes no sense at all. ExecProject can't be expected to access
> output columns of the current node --- they haven't been computed yet.
Conceptionally my only way is then to crack the dependency between the Bar columns by splitting the computation in
differentnodes - and then put these nodes atop of each other.
But then, I still don't get the relationship between
INNER, OUTER varnos on the one side and ecxt_scantuple, ecxt_outertuple and ecxt_innertuple on the other side.
May a non-leaf node refer to a Var with a 'normal' scan varno or only to INNER and OUTER varnos?
How is my Foo node supposed to access the suplan's (whatever that might me, a Scan or a Join) columns? Should Foo'-
tlisthave Vars with OUTER varnos and the right varattos?
I cannot find an example of a node that (1) does projection and (2) is not a Scan (i.e a leaf node) and (3) uses
ecxt_scantupleto pipe information to an upper node.
I'd be happy if you clarified my misconceptions, I greatly appreciate your help.
Regards
Peter
