Re: BUG #17606: There is still some glitch in 3f7323cbb fixing failure of MULTIEXPR_SUBLINK

On Mon, Sep 5, 2022 at 10:25 PM Richard Guo <guofenglinux@gmail.com> wrote:

>
> On Mon, Sep 5, 2022 at 3:33 PM PG Bug reporting form <
> noreply@postgresql.org> wrote:
>
>> 3f7323cbb regenerates its Param for each SubPlan by traversing the
>> targetlist. But ignore one point: initplan is not in targetlist.
>> This will result in a failed assertion, or an error like "unexpected
>> PARAM_MULTIEXPR ID: 131074"
>
>
> Since initplan SubPlans do not have args lists, I think it's OK for them
> to share output parameters. So maybe we do not need to do the
> SS_make_multiexprs_unique trick for initplan SubPlans?
>

If I consider it correctly, can we fix the initplan SubPlan issue simply
as below?

--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -911,6 +911,13 @@ SS_make_multiexprs_unique(PlannerInfo *root,
PlannerInfo *subroot)
                new_multiexpr_params = lappend(new_multiexpr_params,
params);
        }

+       /*
+        * It's OK for initplan SubPlans to share output parameters, so we
do not
+        * need to generate new Param nodes for them.
+        */
+       if (new_multiexpr_params == NIL)
+               return;
+
        /*
         * Now we must find the Param nodes that reference the MULTIEXPR
outputs
         * and update their sublink IDs so they'll reference the new
outputs.

Thanks
Richard