ddl: fix partition definition for literal with non-utf8 charsets + binary column | tidb-test=pr/2262 (#49229)

[ti-chi-bot]

This is an automated cherry-pick of #49229

What problem does this PR solve?

Issue Number: close #36433, close #49251

Problem Summary:

The string literal in the partition clause is stored as a formated string literal. For example, the '你好' will be kept as '你好' in the schema, and the collation information is lost. However, when running the getRangeLocateExprs, the expression is constructed with the DDL session, which always use utf8mb4 collation.

When inserting the row, the string (after converted to the collation corresponding to the column) will be compared with the utf8mb4 literal string, which may cause unexpected behavior. In the issue #36433, the insert value 你好 is converted to binary encoding GBK \xc4\xe3\xba\xc3, and compare it with the utf8 string '你好' through binary collation directly, then former is smaller than the later one.

MySQL records the binary representation in table schema. If we run show create table a in MySQL, it'll give a hex literal with _binary prefix in the partition clause.

What changed and how does it work?

If the target is binary charset, use the hex literal to represent the string. Actually this PR does two change:

1. Always use the evaluated string to represent the partition clause.
2. If the target column collation is binary, use the _binary + hex literal to represent the definition, as it may be an invalid utf8 string.

As TiDB always use utf8 to represent a string internally (except binary), it's fine to not consider other charset like GBK.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Release note

Fix the issue that the partition clause is compared through the collation of `utf8` charset, but not the column charset.

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[YangKeao]

Close, because it will change the behavior.