[KKould]

What problem does this PR solve?

The sql_exec fuzz smoke test panics at histogram.rs:699: on a composite index, a NULL component reports SqlNull, so a bucket ending at (NULL, x) fails debug_assert_eq!(Tuple([Integer, Integer]), Tuple([SqlNull, Integer])). The same strict comparison also made endpoint_count skip keys with NULL components.

Issue link:

What is changed and how it works?

• Add key_types_match: tuple components match when either side is SqlNull; other types still compare exactly.
• Use it for the bucket assertion and for the endpoint type check in endpoint_count.

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer

Repro: index (a, b) with some a IS NULL rows, analyze, then select count(*) from t where a < 193 panics in debug builds. test_endpoint_count_uses_only_full_histogram_keys now covers both cases. The assertion dates from #354; only estimates were affected, not query results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.39%. Comparing base (55e0820) to head (1ae4aee).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #393   +/-   ##
=======================================
  Coverage   93.39%   93.39%           
=======================================
  Files         272      272           
  Lines       39076    39089   +13     
=======================================
+ Hits        36495    36508   +13     
  Misses       2581     2581           

Flag	Coverage Δ
rust	93.39% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/optimizer/core/histogram.rs	94.22% <100.00%> (+0.15%)	⬆️

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