MariaDB doesn't choose DESC index for ORDER BY DESC when MySQL does

# Remove the include if you run the test on MySQL 8.0

--source include/have_innodb.inc

create table t (a int, key aa(a), key ad(a desc)) engine=InnoDB;

insert into t values (1),(5),(2),(8),(4),(6),(7),(9),(3);

explain select * from t order by a desc;

flush status;

select * from t order by a desc;

show status like 'Handler_read%';

# Cleanup

drop table t;

explain select * from t order by a desc;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t	index	NULL	aa	5	NULL	9	Using index

Handler_read_first	0

Handler_read_key	0

Handler_read_last	1

Handler_read_next	0

Handler_read_prev	9

Handler_read_retry	0

Handler_read_rnd	0

Handler_read_rnd_deleted	0

Handler_read_rnd_next	0

explain select * from t order by a desc;

id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t	NULL	index	NULL	ad	5	NULL	10	100.00	Using index

Handler_read_first	1

Handler_read_key	1

Handler_read_last	0

Handler_read_next	9

Handler_read_prev	0

Handler_read_rnd	0

Handler_read_rnd_next	0