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

Hi,

On Mon, Nov 4, 2024 at 12:28 PM jian he <jian.universality@gmail.com> wrote:
>
> 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.

Thanks, yes, a test case that exercises the partcoll1 == exprcoll1
code was missing.

> 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.

Thanks, merged.

-- 
Thanks, Amit Langote