Re: [PATCH] Fix division by zero (explain.c) - Mailing list pgsql-hackers

James Coleman <jtc331@gmail.com> writes:
> There are always full sort groups before any prefix groups can happen,
> so we know (even though the tooling doesn't) that the 2nd test can
> never contradict the first.

So maybe an assertion enforcing that would be appropriate?
Untested, but:

-            if (fullsortGroupInfo->groupCount == 0 &&
-                prefixsortGroupInfo->groupCount == 0)
+            if (fullsortGroupInfo->groupCount == 0)
+            {
+                Assert(prefixsortGroupInfo->groupCount == 0);
                 continue;
+            }

            regards, tom lane