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) ## Which issue does this PR close? - Part of #20766 Related: #20789 (uses NDV for equality filter selectivity, complementary - this PR improves the NDV output stats, that PR consumes them) ## Rationale for this change When a filter predicate collapses a column interval to a single value (e.g. `d_qoy = 1`), the output column can only have one distinct value. Currently `distinct_count` is always demoted to `Inexact`, losing this information. This matters for downstream optimizers that rely on `distinct_count`, such as join cardinality estimation in `estimate_inner_join_cardinality`. ## What changes are included in this PR? In `collect_new_statistics` (filter.rs), when the post-filter interval has `lower == upper` (both non-null), set `distinct_count` to `Precision::Exact(1)` instead of demoting the input NDV to `Inexact`. ## Are these changes tested? Yes, 4 unit tests: - Equality predicate (`a = 42`) -> NDV becomes `Exact(1)` - OR predicate (`a = 42 OR a = 22`) -> interval does not collapse, NDV stays `Inexact` - AND with mixed predicates (`a = 42 AND b > 10 AND c = 7`) -> `a` and `c` get `Exact(1)`, `b` stays `Inexact` - Equality with absent bounds (`a = 42`, no min/max) -> interval analysis still resolves to `Exact(1)` ## Are there any user-facing changes? No breaking changes. Statistics consumers will now see `Exact(1)` for `distinct_count` on columns constrained to a single value by filter predicates. Disclaimer: I used AI to assist in the code generation, I have manually reviewed the output and it matches my intention and understanding. --------- Co-authored-by: xudong.w <wxd963996380@gmail.com>
## Which issue does this PR close? <!-- We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes #123` indicates that this PR will close issue #123. --> - Closes #2976 - Part of #8227 ## Rationale for this change `get_statistics_with_limit` was copying first-file row/byte stats even when`collect_stats=false`. This could return `Exact(0)` instead of `Absent` (unknown stats). <!-- Why are you proposing this change? If this is already explained clearly in the issue then this section is not needed. Explaining clearly why changes are proposed helps reviewers understand your changes and offer better suggestions for fixes. --> ## What changes are included in this PR? Summary stats are only initialized and merged when `collect_stats=true`. Also fixes first-file column `byte_size` initialization in the `collect_stats=true` path, and adds regression tests for both paths and limit behavior. <!-- There is no need to duplicate the description in the issue here but it is sometimes worth providing a summary of the individual changes in this PR. --> ## Are these changes tested? Yes <!-- We typically require tests for all PRs in order to: 1. Prevent the code from being accidentally broken by subsequent changes 2. Serve as another way to document the expected behavior of the code If tests are not included in your PR, please explain why (for example, are they covered by existing tests)? --> ## Are there any user-facing changes? <!-- If there are user-facing changes then we may require documentation to be updated before approving the PR. --> <!-- If there are any breaking changes to public APIs, please add the `api change` label. --> --------- Co-authored-by: Siew Kam Onn <kosiew@gmail.com>
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