expression: fix wrong result type for greatest/least (#29408)

[ti-srebot]

cherry-pick #29408 to release-5.2
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/29914

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git push git@github.com:ti-srebot/tidb.git pr/29914:release-5.2-4b110036e1a7

---

Signed-off-by: guo-shaoge shaoge1994@163.com

What problem does this PR solve?

Issue Number: close #29019

Problem Summary:

1. When all arguments types for greatest/least are datetime, we deduce the result type as string incorrectly.

What's changed:

1. So we need to add four new function sigs for duration and time(builtinGreatestDurationSig, builtinGreatestTimeSig, builtinLeastDurationSig, builtinLeastTimeSig).
2. Also we change the original sig to builtinGreatestCmpStringAsDatetime/builtinLeastCmpStringAsDatetime, because the original sig name is not reasonable.

TODO:

1. When arguments of greatest/least are mixed with time, duration, string, the result is not compitable with mysql. Such as select least(cast('-800:10:10' as time), cast('2021-10-10 10:10:10.1234' as datetime), '99999999999') from t1;

What is changed and how it works?

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 wrong result type for greatest/least

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu

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[ti-srebot]

/run-all-tests

[ti-srebot]

@guo-shaoge you're already a collaborator in bot's repo.

[XuHuaiyu]

LGTM

[guo-shaoge]

Also need to merge #31160 ,otherwise may introduce new problem #29019 .