[MDEV-27330] Wrong sorting order with DESC index and empty strings in MyISAM/Aria table - Jira

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CREATE TABLE t (id int, c char(128) NOT NULL, KEY (c DESC)) ENGINE=MyISAM CHARSET latin1;

INSERT INTO t VALUES (1,''),(2,'foo'),(3,''),(4,'bar');

SELECT c FROM t ORDER BY c;

# Cleanup

DROP TABLE t;

preview-10.8-MDEV-13756-desc-indexes 47c18283
MariaDB [test]> SELECT c FROM t ORDER BY c;
+-----+
\| c \|
+-----+
\| bar \|
\| foo \|
\| \|
\| \|
+-----+
4 rows in set (0.000 sec)

So, the empty strings go last, contrary to the expectation.
Reproducible with MyISAM and Aria.
Not reproducible with InnoDB.

is caused by

MDEV-13756 Implement descending index: KEY (a DESC, b ASC)

relates to

MDEV-27303 Table corruption after insert into a non-InnoDB table with DESC index

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