[BugFix] Preserve null fractions for outer join columns

[OliLay]

Why I'm doing:

Consider the following query:

explain costs
select
    *
from
    TABLE1 t1
    LEFT JOIN TABLE2 t2 ON t1.NULLABLE = t2.NULLABLE
    LEFT JOIN TABLE3 t3 ON t1.NULLABLE = t3.NULLABLE;

At the moment, even though t1.NULLABLE has proper null fractions (e.g. 0.8), the second join assumes that t1.NULLABLE has 0.0 null fractions. This is because for equality predicates, we reset the null fractions to 0 since NULLs are not preserved. In the context of the predicate (and inner joins) this is right, but outer joins should not reset null fractions. Subsequent joins should re-use the original column null fractions instead.

See the following EXPLAIN where the in the topmost join (7) 4: NULLABLE has 0 null fractions, while for the joins prior to that join the correct null fractions are shown. The fixed EXPLAIN contains the proper null fractions for 4: NULLABLE

Wrong null fractions lead to the join not being rewritten, e.g. by the join skew rule.

What I'm doing:

For outer joins, do not reset the null fractions of columns used in join predicates.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5
  • 3.4

[CelerData-Reviewer]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 486f5e06f8

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 15 / 15 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	com/starrocks/sql/optimizer/statistics/StatisticsCalculator.java	15	15	100.00%	[]

[github-actions]

[BE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud