On 26.09.25 22:18, Tom Lane wrote:
Got it, mostly. There is an edge case, though: what if there are no
candidate grouping items? I see these test cases in David's patch:
+-- oops all aggregates
+EXPLAIN (COSTS OFF) SELECT COUNT(a), SUM(b) FROM t1 GROUP BY ALL;
+ QUERY PLAN
+----------------------
+ Aggregate
+ -> Seq Scan on t1
+(2 rows)
+
+-- empty column list
+EXPLAIN (COSTS OFF) SELECT FROM t1 GROUP BY ALL;
+ QUERY PLAN
+----------------
+ Seq Scan on t1
+(1 row)
That is, in such cases the patch behaves as if there were no GROUP BY
clause at all, which seems kinda dubious. Should this be an error,
and if not what's it supposed to do?
These should resolve to GROUP BY ().
Also, what about window functions in the tlist?
(I didn't stop to figure out why this isn't giving the same error, but
maybe it's an order-of-checks thing.) In any case: should this give
"window functions are not allowed in GROUP BY", or should the
window-function-containing tlist item be silently skipped by GROUP BY
ALL? Trying to make it work is surely not the right answer.
Hmm, I don't know. The syntactic transformation talks about select list
elements that "do not directly contain an <aggregate function>", but
that can also appear as part of <window function>, so the syntactic
transformation might appear to apply only to some types of window
functions, which doesn't make sense to me.
I don't know what a sensible behavior should be here. Maybe in this
first patch version just reject use of GROUP BY ALL if you find any
window functions in the select list.
