expression: fix the collation of functions with json arguments

[YangKeao]

What problem does this PR solve?

Issue Number: close #52833

Problem Summary:

MySQL will use binary collation when the max_length of some arguments' types are too long. It'll mostly happen on JSON types.

What changed and how does it work?

As TiDB doesn't have a max_length attribute for each type and "datum", I specially handled the situation for JSON. Some function will return binary collation when some of the arguments are JSON type.

In MySQL, the state of BINARY flag, BLOB type and binary collation is really a chaos. For this example, you'll find that sometimes the collation(...) returns utf8mb4_bin while the returned type info (shown through --column-type-info) tells you the collation is utf8mb4_0900_ai_ci. I'm not sure whether it's a bug for MySQL or not...

So, I want to fix the behavior with minimum modification: only change the collation to binary collation and don't touch the charset.

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.

Fix the issue that the collation of the result of some functions are not compatible with MySQL when the arguments contain JSON.

[codecov]

Codecov Report

Attention: Patch coverage is 97.43590% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 74.5693%. Comparing base (788d505) to head (f90772c).
Report is 30 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #53126        +/-   ##
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+ Coverage   74.4098%   74.5693%   +0.1595%     
================================================
  Files          1490       1492         +2     
  Lines        356051     436989     +80938     
================================================
+ Hits         264937     325860     +60923     
- Misses        71835      91088     +19253     
- Partials      19279      20041       +762     

Flag	Coverage Δ
integration	49.2414% <82.0512%> (?)
unit	71.2585% <92.3076%> (-1.9139%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (-2.3014%)	⬇️
parser	∅ <ø> (∅)
br	50.0550% <ø> (+7.1665%)	⬆️

[YangKeao]

/retest

[YangKeao]

/retest

[YangKeao]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lcwangchao, XuHuaiyu

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

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Needs approval from an approver in each of these files:

• OWNERS [XuHuaiyu,lcwangchao]
• pkg/expression/OWNERS [XuHuaiyu]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-11 04:46:40.952235368 +0000 UTC m=+1282954.709370939: ☑️ agreed by lcwangchao.
• 2024-05-11 08:33:32.403930292 +0000 UTC m=+1296566.161065860: ☑️ agreed by XuHuaiyu.

[YangKeao]

/retest

[YangKeao]

/retest

[YangKeao]

/retest

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #53199.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #53200.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #53201.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #53202.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #53203.