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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_str.test
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@ -474,7 +474,7 @@ where collation(t2.a) = _utf8'binary' order by t1.a,t2.a;
select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
where charset(t2.a) = _utf8'binary' order by t1.a,t2.a;
select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
where coercibility(t2.a) = 6 order by t1.a,t2.a;
where coercibility(t2.a) = 7 order by t1.a,t2.a;
DROP TABLE t1, t2;
#