[MDEV-27586] Auto-increment does not work with DESC on MERGE table - Jira

create table t (a int not null, primary key(a desc)) engine=MyISAM;

create table tm (a int not null auto_increment, primary key(a desc)) engine=MERGE union=(t) insert_method=FIRST;

insert into tm () values ();

insert into tm () values ();

insert into tm () values ();

drop table tm, t;

The third INSERT above fails with

preview-10.8-MDEV-13756-desc-indexes c10e10c6
At line 6: query 'insert into tm () values ()' failed: ER_DUP_ENTRY (1062): Duplicate entry '2' for key 'PRIMARY'

Not reproducible with an ascending key.

is caused by

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

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