Re: Wrong result when enable_partitionwise_join is on if collation of PartitionKey and Column is different.

just a quick reply while testing v4-0001.
tests copy from src/test/regress/sql/partition_aggregate.sql first 40 lines.

drop table if exists pagg_tab;
CREATE TABLE pagg_tab (a int, b int, c text, d int) PARTITION BY
LIST(c collate "C");
CREATE TABLE pagg_tab_p1 PARTITION OF pagg_tab FOR VALUES IN ('0000',
'0001', '0002', '0003', '0004');
CREATE TABLE pagg_tab_p2 PARTITION OF pagg_tab FOR VALUES IN ('0005',
'0006', '0007', '0008');
CREATE TABLE pagg_tab_p3 PARTITION OF pagg_tab FOR VALUES IN ('0009',
'0010', '0011');
INSERT INTO pagg_tab SELECT (i % 20), (i % 30), to_char(i % 12,
'FM0000'), i % 30 FROM generate_series(0, 2999) i;
ANALYZE pagg_tab;

EXPLAIN (COSTS OFF, settings)
SELECT a, sum(b), avg(b), count(*), max(b) FROM pagg_tab GROUP BY a;


 QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------------
 Finalize HashAggregate
   Group Key: pagg_tab.a
   ->  Append
         ->  Partial HashAggregate
               Group Key: pagg_tab.a
               ->  Seq Scan on pagg_tab_p1 pagg_tab
         ->  Partial HashAggregate
               Group Key: pagg_tab_1.a
               ->  Seq Scan on pagg_tab_p2 pagg_tab_1
         ->  Partial HashAggregate
               Group Key: pagg_tab_2.a
               ->  Seq Scan on pagg_tab_p3 pagg_tab_2
 Settings: enable_partitionwise_aggregate = 'on',
enable_partitionwise_join = 'on', max_parallel_workers_per_gather =
'0', enable_increm
ental_sort = 'off'



drop table if exists pagg_tab;
CREATE TABLE pagg_tab (a text, b int, c text, d int) PARTITION BY
LIST(c collate "C");
CREATE TABLE pagg_tab_p1 PARTITION OF pagg_tab FOR VALUES IN ('0000',
'0001', '0002', '0003', '0004');
CREATE TABLE pagg_tab_p2 PARTITION OF pagg_tab FOR VALUES IN ('0005',
'0006', '0007', '0008');
CREATE TABLE pagg_tab_p3 PARTITION OF pagg_tab FOR VALUES IN ('0009',
'0010', '0011');
INSERT INTO pagg_tab SELECT (i % 20)::text, (i % 30), to_char(i % 12,
'FM0000'), i % 30 FROM generate_series(0, 2999) i;
ANALYZE pagg_tab;
EXPLAIN (COSTS OFF, settings)
SELECT a, sum(b), avg(b), count(*), max(b) FROM pagg_tab GROUP BY a;


 QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------------
 HashAggregate
   Group Key: pagg_tab.a
   ->  Append
         ->  Seq Scan on pagg_tab_p1 pagg_tab_1
         ->  Seq Scan on pagg_tab_p2 pagg_tab_2
         ->  Seq Scan on pagg_tab_p3 pagg_tab_3
 Settings: enable_partitionwise_aggregate = 'on',
enable_partitionwise_join = 'on', max_parallel_workers_per_gather =
'0', enable_increm
ental_sort = 'off'


it seems "PARTITION BY LIST(c collate "C");" collation compare with
"GROUP BY a;".
set collation_incompatible returned true.
make it cannot do PARTITIONWISE_AGGREGATE_PARTIAL.

but here "group by a", "a" is text data type, we can still do
PARTITIONWISE_AGGREGATE_PARTIAL
?