time: fix the fraction loss when encountering time string with timezone suffix (#37820)

[ti-srebot]

cherry-pick #37820 to release-6.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/38010

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/38010:release-6.2-b8d929c3c754

---

What problem does this PR solve?

Issue Number: close #35291

Problem Summary:

What is changed and how it works?

Identify the position of the timezone before identifying the position of the fraction in the time string to avoid the accuracy loss. Timezone will also be checked later to ensure compatibility so that there is duplicate detection for timezone.

Check List

Tests

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

DROP TABLE IF EXISTS `testSetObjectTime`;
CREATE TABLE `testSetObjectTime` (
  `id` int(11) DEFAULT NULL,
  `d` time(6) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;
INSERT INTO testSetObjectTime VALUES (1, '2020-01-01 12:00:00.123456000+05:00');
INSERT INTO testSetObjectTime VALUES (2, '2020-01-01 12:00:00.123456+05:00');
SELECT * FROM testSetObjectTime;

+------+-----------------+
| id   | d               |
+------+-----------------+
|    1 | 15:00:00.123456 |
|    2 | 15:00:00.123456 |
+------+-----------------+

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

[ti-chi-bot]

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[ti-srebot]

/run-all-tests

[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

@Qiaolin-Yu you're already a collaborator in bot's repo.

[wuhuizuo]

/run-check-dev

[wuhuizuo]

/run-check_dev

[wuhuizuo]

/run-check-dev