expression: Fix the bug that castStringAsReal has different behaivor between tiflash and tikv/tidb.

[LittleFall]

What problem does this PR solve?

Issue Number: close #3475, related to #3447

Problem Summary: Fix the bug that castStringAsReal has different behaivor between tiflash and tikv/tidb.

What is changed and how it works?

truncate string, instead of passing it all to strtod.

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

Fix the issue that `castStringAsReal` behavior is inconsistent in TiFlash and in TiDB/TiKV

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• windtalker

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[windtalker]

LGTM

[LittleFall]

/merge

[ti-chi-bot]

@LittleFall: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[windtalker]

/merge

[ti-chi-bot]

@windtalker: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

If you have any questions about the PR merge process, please refer to pr process.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

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

Commit hash: 183d9d1

[sre-bot]

Coverage detail: https://ci-internal.pingcap.net/job/tics_ghpr_unit_test/653/cobertura/
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[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3753.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3754.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3755.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3756.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #3757.

[sre-bot]

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