sink/mysql: explicit_defaults_for_timestamp compatibility with mysql (#1638)

[ti-srebot]

cherry-pick #1638 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In ticdc repo:
git pr https://github.com/pingcap/ticdc/pull/1658

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

git push [email protected]:ti-srebot/ticdc.git pr/1658:release-4.0-6d4d4e4faead

---

What problem does this PR solve?

Fix #1585

What is changed and how it works?

• Set session variable explicit_defaults_for_timestamp to ON in MySQL sink, which will keep the same behavior between upstream TiDB and downstream MySQL 5.7.
• Note only set this session variable when the value explicit_defaults_for_timestamp in downstream is OFF, because in TiDB variable explicit_defaults_for_timestamp is readonly.

Check List

Tests

• Unit test
• Integration test

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release note

• Set session variable explicit_defaults_for_timestamp to ON to make downstream MySQL5.7 keeps the same behavior with upstream TiDB.

[ti-srebot]

/run-all-tests

[amyangfei]

/run-all-tests

[amyangfei]

/run-all-tests

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• leoppro

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[amyangfei]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d297e09

[codecov-commenter]

Codecov Report

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