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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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2
mysql-test/main/func_time.result
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@ -616,7 +616,7 @@ LOWER(MONTHNAME(19700101))
january
SELECT COERCIBILITY(MONTHNAME('1970-01-01')),COERCIBILITY(DAYNAME('1970-01-01'));
COERCIBILITY(MONTHNAME('1970-01-01')) COERCIBILITY(DAYNAME('1970-01-01'))
5 5
6 6
CREATE TABLE t1 (datetime datetime, timestamp timestamp, date date, time time);
INSERT INTO t1 values ("2001-01-02 03:04:05", "2002-01-02 03:04:05", "2003-01-02", "06:07:08");
SELECT * from t1;