cherry-pick #1903 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tics repo:
git pr https://github.com/pingcap/tics/pull/1914

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tics.git pr/1914:release-4.0-b40059d50ca7

What problem does this PR solve?

Issue Number: close #1184

Problem Summary:
The root cause is that SubstringUTF8 function in TiFlash doesn't correcly handle the case pos is a negative value and its absolute value is greater than length of input string.

What is changed and how it works?

Proposal: xxx

What's Changed:

Related changes

• Need to cherry-pick to the release branch:

Check List

Tests

• Integration test

Release note

• Fix the problem that TiFlash will crash when executing SUBSTRING function with specific argument