planner: address collation ambiguity in scalar function construction during predicate simplification. (#57049)

[ti-chi-bot]

This is an automated cherry-pick of #57049

What problem does this PR solve?

Issue Number: close #56479

Problem Summary:

What changed and how does it work?

We can simplify the sql as follows:

DROP TABLE t1;

CREATE TABLE t1 (
c1 VARCHAR(175) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT 'asMF'
);

SELECT *
FROM t1
WHERE c1 BETWEEN 'string1' AND 'string2' AND (c1 = 'string3' OR IsNull(c1));

When rewriting the BETWEEN and AND clause, the collations of string1 and string2 will be set to c1's collation—utf8mb4_unicode_ci rather than collation_connection.

During predicate simplification, a scalar function 'ge' will be constructed using string1 and string3 as parameters. However, since string1 has a collation of utf8mb4_unicode_ci and string3 has a collation of utf8mb4_general_ci (collation_connection), and both of them have a coercibility of 4, there is ambiguity regarding which collation to use. This leads to an failure to construct a new scalar function, which will lead a panic.

There's an additional concern: if we replace "BETWEEN and AND" with "<= and >=", then both string1 and string3 have a collation of utf8mb4_general_ci(collation_connection), then during predicate simplification, string1 and string3 would be compared using the utf8mb4_general_ci collation. This might lead to potential incorrect results.

Maybe we can:

During predicate simplification, we could reset the collation of the constants (string1, string2, string3) to match the collation of the column c1 to address the problems.

Check List

Tests

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

  • I checked and no code files have been changed.

Side effects

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

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5@08ed793). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #57476   +/-   ##
================================================
  Coverage               ?   56.9861%           
================================================
  Files                  ?       1770           
  Lines                  ?     625943           
  Branches               ?          0           
================================================
  Hits                   ?     356701           
  Misses                 ?     245134           
  Partials               ?      24108           

Flag	Coverage Δ
integration	36.8313% <66.6666%> (?)
unit	72.6432% <33.3333%> (?)

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

Components	Coverage Δ
dumpling	52.9478% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.4564% <0.0000%> (?)

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests
• JS Bundle Analysis - Avoid shipping oversized bundles

[fixdb]

+1

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, fixdb

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [AilinKid,fixdb]
• pkg/planner/OWNERS [AilinKid,fixdb]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-11-19 01:34:24.283963879 +0000 UTC m=+924826.474832876: ☑️ agreed by AilinKid.
• 2024-11-19 06:00:15.289798339 +0000 UTC m=+940777.480667336: ☑️ agreed by fixdb.