Re: Analyze plan of foreign data wrapper

I read it many times but I'am not entirely familiar with concepts of range
table and I'am not sure to fully understant all implications.
For now I have a workaround by parsing only plan's target list and by
checking if resorigtbl is equal to oid of my table. The main drawback is
that I can't detect column if it is used in a function or an aggregator.
Thanks anyway for your help.

Le mar. 3 juil. 2018 à 12:38, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> a
écrit :

> Mathieu PUJOL wrote:
> > I understand that I should also use varno to check which table is
> referenced by varattno. In case of Join, aggregation, etc. Sometimes I get
> a number or INNER_VAR or OUTER_VAR.
> > I am lost on how i could resolve this.
> > I understand that OUTER_VAR/INNER_VAR are related to joins sub plans. Is
> outer related to left plan and inner to right plan ? In this case varattno
> is index of target list of subplan ?
> > When varno is an index how to retrieve table info ?
>
> I have no deep understanding of these things.
>
> Maybe the following comment from include/nodes/primnodes.h can help:
>
> /*
> * Var - expression node representing a variable (ie, a table column)
> *
> * Note: during parsing/planning, varnoold/varoattno are always just copies
> * of varno/varattno. At the tail end of planning, Var nodes appearing in
> * upper-level plan nodes are reassigned to point to the outputs of their
> * subplans; for example, in a join node varno becomes INNER_VAR or
> OUTER_VAR
> * and varattno becomes the index of the proper element of that subplan's
> * target list. Similarly, INDEX_VAR is used to identify Vars that
> reference
> * an index column rather than a heap column. (In ForeignScan and
> CustomScan
> * plan nodes, INDEX_VAR is abused to signify references to columns of a
> * custom scan tuple type.) In all these cases, varnoold/varoattno hold
> the
> * original values. The code doesn't really need varnoold/varoattno, but
> they
> * are very useful for debugging and interpreting completed plans, so we
> keep
> * them around.
> */
> #define INNER_VAR 65000 /* reference to inner subplan */
> #define OUTER_VAR 65001 /* reference to outer subplan */
> #define INDEX_VAR 65002 /* reference to index column */
>
> #define IS_SPECIAL_VARNO(varno) ((varno) >= INNER_VAR)
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com
>