Re: POC: GROUP BY optimization

hi
one more question (maybe a dumb one....)

drop table if exists t1;
CREATE TABLE t1 AS
  SELECT (i % 10)::numeric AS x,(i % 10)::int8 AS y,'abc' || i % 10 AS
z, i::int4 AS w
  FROM generate_series(1, 100) AS i;
CREATE INDEX t1_x_y_idx ON t1 (x, y);
ANALYZE t1;
SET enable_hashagg = off;
SET enable_seqscan = off;


EXPLAIN (COSTS OFF, verbose) SELECT count(*) FROM t1 GROUP BY z,x,y,w
order by w;


                      QUERY PLAN
------------------------------------------------------
 GroupAggregate
   Output: count(*), w, z, x, y
   Group Key: t1.w, t1.x, t1.y, t1.z
   ->  Sort
         Output: w, z, x, y
         Sort Key: t1.w, t1.x, t1.y, t1.z
         ->  Index Scan using t1_x_y_idx on public.t1
               Output: w, z, x, y
(8 rows)


if you do
` Sort Key: t1.w, t1.x, t1.y, t1.z`

then the output is supposed to be:

Output: w, x, y, z

?