executor: fix split table with large integers

[tangenta]

What problem does this PR solve?

Problem Summary:

create table t(a bigint(20) auto_increment primary key);
split table t between (-9223372036854775808) and (9223372036854775807) regions 16;

TiDB tries to calculate the splitting point with (max-min)/region_num. In the case above, the result is 0 and it violates the constraint(the step should be greater than 1000).

What is changed and how it works?

What's Changed:

• Convert int64 to uint64 before calculating the split region step.
• Refine the error message about splitting regions.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Side effects

N/A

Release note

• Fix the issue that split table between large integers failed.

[AilinKid]

LGTM

[ti-chi-bot]

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[AilinKid]

/lgtm

[crazycs520]

LGTM

[ti-chi-bot]

@crazycs520: Please use /LGTM instead of LGTM when you want to approve the pull request by comment.
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[crazycs520]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• crazycs520

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[tangenta]

/merge

[tangenta]

/merge cancel

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: 45de1c3

[ti-chi-bot]

@tangenta: Your PR was out of date, I have automatically updated it for you.

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/run-all-tests

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