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MDEV-35041 Simple comparison causes "Illegal mix of collations" even with default server settings

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The task "MDEV-25829 Change default Unicode collation to uca1400_ai_ci"
previously changed collation derivation for string user variables
from DERIVATION_EXPLICIT to DERIVATION_COERCIBLE, to resolve illegal
collation mix conflicts between table columns and user variables
when they have different collations.

However, DERIVATION_COERCIBLE was a wrong choice because it caused
conflicts between string literals and user variables when they have
different collations.

Adding a new collation derivation level DERIVATION_USERVAR.
This makes the collation of a user variable:
- weaker than a table column (like it was intended by MDEV-25829)
- but stronger than a literal (like it was in pre-MDEV-25829)

Cleanup in sql_type.h:
  Removing the line "- BINARY(expr)" from the before-DERIVATION_CAST
  comment, as it was on a wrong place. It's also listed on the correct
  place before DERIVATION_IMPLICIT.
This commit is contained in:
Alexander Barkov
2024-10-22 11:10:58 +04:00
parent 4e1e9ea6f3
commit a88c71b294
31 changed files with 178 additions and 117 deletions
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4
mysql-test/main/func_misc.result
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@ -1477,10 +1477,10 @@ COERCIBILITY(NAME_CONST('name','test'))
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SELECT COERCIBILITY(NAME_CONST('name',TIME'00:00:00'));
COERCIBILITY(NAME_CONST('name',TIME'00:00:00'))
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SELECT COERCIBILITY(NAME_CONST('name',15));
COERCIBILITY(NAME_CONST('name',15))
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SELECT CONCAT(NAME_CONST('name',15),'오');
CONCAT(NAME_CONST('name',15),'오')
15오