sql-statement: refine the sqlgram for alter table

[tangenta]

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

/label needs-cherry-pick-release-6.1

[TomShawn]

/remove-status LGT1
/status LGT2

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 4c4138a

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #9760.