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

hi.
about v5.
if (exprs_known_equal(root, expr1, expr2, btree_opfamily))
{
/*
* Ensure that the collation of the expression matches
* that of the partition key. Checking just one collation
* (partcoll1 and exprcoll1) suffices because partcoll1
* and partcoll2, as well as exprcoll1 and exprcoll2,
* should be identical. This holds because both rel1 and
* rel2 use the same PartitionScheme and expr1 and expr2
* are equal.
*/
if (partcoll1 == exprcoll1)
{
Oid partcoll2 PG_USED_FOR_ASSERTS_ONLY =
rel1->part_scheme->partcollation[ipk];
Oid exprcoll2 PG_USED_FOR_ASSERTS_ONLY =
exprCollation(expr2);
Assert(partcoll2 == exprcoll2);
pk_known_equal[ipk] = true;
if (OidIsValid(exprcoll1))
elog(INFO, "this path called %s:%d",
__FILE_NAME__, __LINE__);
break;
}
}

tests still passed, which means that we didn't have text data type as
partition key related tests for partition-wise join.
Do we need to add one?

+-- Another case where the partition keys are matched via equivalence class,
+-- not a join restriction clause.
+
+-- OK when the join clause uses the same collation as the partition key
+EXPLAIN (COSTS OFF)
+SELECT t1.c, count(t2.c) FROM pagg_tab3 t1 JOIN pagg_tab4 t2 ON t1.c
= t2.c AND t1.c = t2.b COLLATE "C" GROUP BY 1 ORDER BY 1;

i suppose, you comments is saying that in have_partkey_equi_join
the above query will return true via
`if (exprs_known_equal(root, expr1, expr2, btree_opfamily))`
But " t1.c = t2.b COLLATE "C" already in "restrictlist".
In have_partkey_equi_join loop through "restrictlist" would return
true for above query, won't reach exprs_known_equal.

Other than the comments that confused me, the test and the results
look fine to me.

some column collation is case_insensitive, ORDER BY that column would
render the output not deterministic.
like 'A' before 'a' and 'a' before 'A' are both correct.
it may cause regress tests to fail.
So I did some minor refactoring to make the "ORDER BY" deterministic.