[jayzhan211]

Which issue does this PR close?

• None. Related to test: add planner tests for ordering, constant and equality facts #26570 and refactor: derive cross join equivalence properties as an inner join #26631, which also work on how equivalence properties pass through operators.

Rationale for this change

Operators that combine rows from several input partitions must forget the facts that hold only inside each
partition: constants whose value may differ between partitions, and, unless the operator keeps order, the input's
orderings. Today this rule is written out in four places, and the copies disagree when the input has a single
partition:

	One input partition	Several input partitions
RepartitionExec	keeps everything	drops per-partition constants, and orderings unless order-preserving
join-key alignment in EnforceDistribution	keeps everything	drops per-partition constants
SortPreservingMergeExec	drops per-partition constants	drops per-partition constants
CoalescePartitionsExec	drops per-partition constants and orderings	drops per-partition constants and orderings

With one input partition, both SortPreservingMergeExec and CoalescePartitionsExec pass the input stream
through, so nothing they drop has stopped being true.

What changes are included in this PR?

• EquivalenceProperties::merged(input_partitions, keeps_order): with one input partition everything is kept;
  otherwise per-partition constants are dropped, and orderings too unless keeps_order.
• The four places above call it.

What is the testing strategy for this PR?

• A unit test for merged: one partition against two, with and without keeps_order.
• A test that CoalescePartitionsExec over one sorted partition reports that ordering (it fails before this
  change) and over two does not.
• Existing tests, including all sqllogictests, pass without changes; no plan changes.

Are there any user-facing changes?

SortPreservingMergeExec and CoalescePartitionsExec over a single input partition keep the facts of their
input, so the planner may skip a sort it does not need. Results do not change. New public method
EquivalenceProperties::merged.

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
    Building datafusion-physical-expr v55.1.0 (current)
       Built [  48.805s] (current)
     Parsing datafusion-physical-expr v55.1.0 (current)
      Parsed [   0.059s] (current)
    Building datafusion-physical-expr v55.1.0 (baseline)
       Built [  33.663s] (baseline)
     Parsing datafusion-physical-expr v55.1.0 (baseline)
      Parsed [   0.058s] (baseline)
    Checking datafusion-physical-expr v55.1.0 -> v55.1.0 (no change; assume patch)
     Checked [   0.347s] 229 checks: 228 pass, 1 fail, 0 warn, 31 skip

--- failure function_missing: pub fn removed or renamed ---

Description:
A publicly-visible function cannot be imported by its prior path. A `pub use` may have been removed, or the function itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.51.0/src/lints/function_missing.ron

Failed in:
  function datafusion_physical_expr::intervals::utils::check_statistics_support, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/cf2444ffe425aa529f39ab196963d20d5a56340a/datafusion/physical-expr/src/intervals/utils.rs:46

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [  83.857s] datafusion-physical-expr
    Building datafusion-physical-optimizer v55.1.0 (current)
       Built [  45.463s] (current)
     Parsing datafusion-physical-optimizer v55.1.0 (current)
      Parsed [   0.021s] (current)
    Building datafusion-physical-optimizer v55.1.0 (baseline)
       Built [  45.883s] (baseline)
     Parsing datafusion-physical-optimizer v55.1.0 (baseline)
      Parsed [   0.022s] (baseline)
    Checking datafusion-physical-optimizer v55.1.0 -> v55.1.0 (no change; assume patch)
     Checked [   0.123s] 229 checks: 229 pass, 31 skip
     Summary no semver update required
    Finished [  92.699s] datafusion-physical-optimizer
    Building datafusion-physical-plan v55.1.0 (current)
       Built [  43.502s] (current)
     Parsing datafusion-physical-plan v55.1.0 (current)
      Parsed [   0.235s] (current)
    Building datafusion-physical-plan v55.1.0 (baseline)
       Built [  43.966s] (baseline)
     Parsing datafusion-physical-plan v55.1.0 (baseline)
      Parsed [   0.238s] (baseline)
    Checking datafusion-physical-plan v55.1.0 -> v55.1.0 (no change; assume patch)
     Checked [   0.686s] 229 checks: 229 pass, 31 skip
     Summary no semver update required
    Finished [  89.859s] datafusion-physical-plan