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MDEV-7649 wrong result when comparing utf8 column with an invalid literal


Hi Sergei,

I tested comparison behaviour for various different situations.

Please find the comment with the summary table in the end of:

Currently there are 5 possible reactions on bad bytes on comparison,
depending on the collation, presence of an index, and character_set_connection value:

- truncate on bad byte, compare only the well-formed prefix (#1)
- treat bad bytes as '?' (#7 and #8)
- empty set with no warning (#3)
- empty set with a warning (#2)
- error (#5 and #6)

I'm in doubts what to dofor 10.1 and for 5.5. Please suggest.

1. For 10.1 or 10.2 I think it would be nice to make all these cases
work  exactly the same way. I am not sure which way would be the best.
Any ideas?

2. For 5.5 we need to fix the bug with minimal changes. Do you agree?
I suggest we fix only #1 and maybe #2.

How we fix 5.5 now should probably depend on how we'll fix 10.1,
to avoid changing behaviour many times. Please suggest.


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