[GLUTEN-12834][CH] Fix nullable filtering after Expand with constant columns

[exmy]

What changes are proposed in this pull request?

This PR fixes incorrect nullable filtering after Expand in the ClickHouse backend.

The changes:

• Materialize constant selection columns in regular Expand.
• Apply the same behavior to AdvancedExpand.
• Preserve nullable types for NULL literals.
• Add regression tests for both regular and lazy aggregate Expand paths.

Expand emits each grouping-set projection as a separate chunk.

When a selected input column originates from a SQL literal, castColumn may preserve it as a ColumnConst. In the reproducing query, the first chunk contains a constant non-null msg_type, so isNotNull(msg_type) produces a constant true filter.

The ClickHouse FilterTransform version used by the backend preserves ConstantFilterDescription between chunks. It checks the previous always_true state before recalculating the filter for the current chunk.

As a result, the following chunk, whose msg_type is a real nullable NULL, can bypass filtering and produce extra grouping-set rows.

For example:

select msg_type, os, count(*) as cnt
from (
  select 'file' as msg_type, 'Android' as os, id from range(10)
  union all
  select 'file' as msg_type, 'iOS' as os, id from range(10)
) t
group by grouping sets ((msg_type), (os))
having msg_type is not null
order by msg_type, os, cnt

the incorrect result was:

NULL  Android  10
NULL  iOS      10
file  NULL     20

The expected result is:

file  NULL  20

Materialize constant selection columns in regular and advanced Expand to prevent stale constant filter state from leaking null rows. Preserve nullable types for null literals and add regression coverage for both Expand paths.

How was this patch tested?

add ut

Was this patch authored or co-authored using generative AI tooling?

Codex

close #12834

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[Copilot]

Pull request overview

This PR fixes a ClickHouse backend correctness issue where Expand could emit constant columns that caused stale constant-filter state to leak across chunks, allowing rows with nullable NULL values to bypass is not null filtering. It does so by materializing constant selection columns in both regular and advanced Expand paths, preserving nullability for NULL literals, and adding regression tests covering both regular and lazy-aggregate Expand plans.

Changes:

• Preserve nullable output types for NULL literals in Expand projections.
• Materialize constant selection columns produced by castColumn in both ExpandTransform and AdvancedExpandTransform.
• Add regression tests validating grouping-sets + having ... is not null behavior for both regular and lazy aggregate Expand.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
cpp-ch/local-engine/Parser/RelParsers/ExpandRelParser.cpp	Ensures NULL literals remain nullable in Expand output types to produce a real null map.
cpp-ch/local-engine/Operator/ExpandTransform.cpp	Converts casted selection results to full columns when they’re constant to prevent per-chunk constant filter leakage.
cpp-ch/local-engine/Operator/AdvancedExpandStep.cpp	Applies the same const-materialization behavior for AdvancedExpand.
backends-clickhouse/src/test/scala/org/apache/gluten/execution/tpch/GlutenClickHouseTPCHSaltNullParquetSuite.scala	Adds regression coverage for both Expand paths and toggles the runtime flag used by the CH planner.

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.