expression: fix the collation of functions with json arguments (#53126)

[ti-chi-bot]

This is an automated cherry-pick of #53126

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.

[ti-chi-bot]

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@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev	ff42495	link	true	/test check-dev
idc-jenkins-ci-tidb/check_dev_2	ff42495	link	true	/test check-dev2
idc-jenkins-ci-tidb/build	ff42495	link	true	/test build
idc-jenkins-ci-tidb/unit-test	ff42495	link	true	/test unit-test
idc-jenkins-ci-tidb/mysql-test	ff42495	link	true	/test mysql-test

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[YangKeao]

Close, as it'll introduce compatibility breaker.