sync_diff: fix hidden column

[okJiang]

What problem does this PR solve?

Issue Number: close https://github.com/pingcap/tidb-tools/issues/713

What is changed and how it works?

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to be included in the release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth

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[lance6716]

@okJiang Can you add a test, or manually test it?

[okJiang]

@okJiang Can you add a test, or manually test it?

This PR has not yet solved this issue, and it has been manually tested.

@Leavrth will take a look for this in Friday

[ti-chi-bot]

@YangKeao: Thanks for your review. The bot only counts approvals from reviewers and higher roles in list, but you're still welcome to leave your comments.

In response to [this](https://github.com/pingcap/tidb-tools/pull/712#pullrequestreview-1364361662): >LGTM Instructions for interacting with me using PR comments are available [here](https://prow.tidb.net/command-help). If you have questions or suggestions related to my behavior, please file an issue against the [ti-community-infra/tichi](https://github.com/ti-community-infra/tichi/issues/new?title=Prow%20issue:) repository.

[YangKeao]

I think https://github.com/pingcap/tidb-tools/pull/715 is part of it, so you need to resolve the conflict.

[Leavrth]

the index having expression is not support for binary search, bucket split and random split features in sync-diff-inspector. So ignore this kind of the index when build splitter.

(However, sync-diff-inspector doesn't compare the index kvs.

[okJiang]

/merge

[ti-chi-bot]

@okJiang: /merge in this pull request requires 1 approval(s).

In response to [this](https://github.com/pingcap/tidb-tools/pull/712#issuecomment-1501593939): >/merge Instructions for interacting with me using PR comments are available [here](https://prow.tidb.net/command-help). If you have questions or suggestions related to my behavior, please file an issue against the [ti-community-infra/tichi](https://github.com/ti-community-infra/tichi/issues/new?title=Prow%20issue:) repository.

[Leavrth]

/merge

[ti-chi-bot]

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

Commit hash: d7a5efd9a3ff08f4222b39496c54ceada003aa2f