Re: Fix error message for MERGE foreign tables

[Richard Guo]

On Fri, Oct 14, 2022 at 5:24 PM Alvaro Herrera <alvhe...@alvh.no-ip.org>
wrote:

> Actually, I hadn't realized that the originally submitted patch had the
> test in postgres_fdw only, but we really want it to catch any FDW, so it
> needs to be somewhere more general.  The best place I found to put this
> test is in make_modifytable ... I searched for some earlier place in the
> planner to do it, but couldn't find anything.
>
> So what do people think about this?


Good point. I agree that the test should be in a more general place.

I wonder if we can make it earlier in grouping_planner() just before we
add ModifyTablePath.

--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -1772,6 +1772,17 @@ grouping_planner(PlannerInfo *root, double
tuple_fraction)
         /* Build per-target-rel lists needed by ModifyTable */
         resultRelations = lappend_int(resultRelations,
                                       resultRelation);
+        if (parse->commandType == CMD_MERGE &&
+            this_result_rel->fdwroutine != NULL)
+        {
+            RangeTblEntry *rte = root->simple_rte_array[resultRelation];
+
+            ereport(ERROR,
+                    errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                    errmsg("cannot execute MERGE on relation \"%s\"",
+                           get_rel_name(rte->relid)),
+                    errdetail_relkind_not_supported(rte->relkind));
+        }

Thanks
Richard