executor: Fix group_concat returns wrong results after set group_concat_max_len

[SeaRise]

What problem does this PR solve?

Issue Number: close #27751

Problem Summary:

What is changed and how it works?

Use heap.pop instead of rows[0] to get the top element of the heap in topNRows::tryToAdd

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

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 group_concat returns wrong results after set group_concat_max_len

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• guo-shaoge

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[sre-bot]

Please follow PR Title Format:

• pkg [, pkg2, pkg3]: what is changed

Or if the count of mainly changed packages are more than 3, use

• *: what is changed

After you have format title, you can leave a comment /run-check_title to recheck it

[sre-bot]

Please follow PR Title Format:

• pkg [, pkg2, pkg3]: what is changed

Or if the count of mainly changed packages are more than 3, use

• *: what is changed

After you have format title, you can leave a comment /run-check_title to recheck it

[SeaRise]

/run-all-tests

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/14b1111420f078cab8d83dc1b7763817e60fc3f3

[SeaRise]

/cc @XuHuaiyu @guo-shaoge

[SeaRise]

/run-unit-test

[SeaRise]

/run-check_dev_2

[ti-srebot]

cherry pick to release-5.0 in PR #35935

[ti-srebot]

cherry pick to release-5.1 in PR #35936

[ti-srebot]

cherry pick to release-5.2 in PR #35937

[ti-srebot]

cherry pick to release-5.3 in PR #35938

[ti-srebot]

cherry pick to release-5.4 in PR #35939

[ti-srebot]

cherry pick to release-6.0 in PR #35940

[ti-srebot]

cherry pick to release-6.1 in PR #35941

[SeaRise]

/review default

[SeaRise]

/review default

[ti-chi-bot]

@SeaRise:

Review of Pull Request: executor: Fix group_concat returns wrong results after set group_concat_max_len

Summary

This pull request fixes a bug where group_concat returns wrong results after setting group_concat_max_len. It uses heap.pop instead of rows[0] to get the top element of the heap in topNRows::tryToAdd.

Key Changes

• Used heap.pop in topNRows::tryToAdd instead of rows[0].
• Other minor changes.

Potential Problems

• No tests for integration and manual testing have been included.
• No new tests for the specific fix have been added.

Suggestions

• Add integration test cases and re-run tests to ensure that other parts of the code weren't affected.
• Add new tests that focus specifically on the fix applied.
• Consider adding more details to the pull request description, such as how results used to be incorrect and what issues this caused.
• Consider changing the release note to include more specific information about the issue (group_concat bug) and what the fix is.

Final Verdict

The changes proposed in this pull request seem to be appropriate and fixes an existing bug. However, it still needs work to be considered safe for merging.

In response to this:

/review default

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[ti-chi-bot]

@SeaRise:
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In response to this:

/review default

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