The bug about case when error is generated is fixed. Error messages are updated to avoid missleadings.

[mariadb-NedeljkoStefanovic]

• The Jira issue number for this PR is: MDEV-______

Description

TODO: fill description here

Release Notes

TODO: What should the release notes say about this change?
Include any changed system variables, status variables or behaviour. Optionally list any https://mariadb.com/kb/ pages that need changing.

How can this PR be tested?

TODO: modify the automated test suite to verify that the PR causes MariaDB to behave as intended.
Consult the documentation on "Writing good test cases".

If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

[CLAassistant]

All committers have signed the CLA.

[vuvova]

this doesn't look right. why prefixed columns are not considered? This looks like a bug that should be fixed, not documented.

[mariadb-NedeljkoStefanovic]

this doesn't look right. why prefixed columns are not considered? This looks like a bug that should be fixed, not documented.

Task description is to generate warnings about prefixes which are ignored. If prefixes have to be supported, then task description is incorrect.

[vuvova]

someone reports a bug. we need to decide how to fix it, we cannot blindly do whatever reporter says. Perhaps, partitioning cannot take into account prefix prefix keys. I don't see why, it looks like a an easy bug to fix to me, but I can be missing something.