create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (
pk int primary key,
a int not null,
b int not null,
key(a) comment 'rev:foo',
key(b) comment 'bar'
) engine=xengine;
insert into t1 select a,a,a  from t0;
insert into t1 select a+10,a+10,a+10  from t0;
# Primary key is not in a reverse-ordered CF, so full table scan
#   returns rows in ascending order:
select * from t1;
pk	a	b
0	0	0
1	1	1
2	2	2
3	3	3
4	4	4
5	5	5
6	6	6
7	7	7
8	8	8
9	9	9
10	10	10
11	11	11
12	12	12
13	13	13
14	14	14
15	15	15
16	16	16
17	17	17
18	18	18
19	19	19
explain 
select a from t1 order by a limit 5;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	NULL	index	NULL	a	4	NULL	#	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` order by `test`.`t1`.`a` limit 5
select a from t1 order by a limit 5;
a
0
1
2
3
4
explain 
select b from t1 order by b limit 5;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	NULL	index	NULL	b	4	NULL	#	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t1`.`b` AS `b` from `test`.`t1` order by `test`.`t1`.`b` limit 5
select a from t1 order by a limit 5;
a
0
1
2
3
4
explain 
select a from t1 order by a desc limit 5;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	NULL	index	NULL	a	4	NULL	#	100.00	Backward index scan; Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` order by `test`.`t1`.`a` desc limit 5
select a from t1 order by a desc limit 5;
a
19
18
17
16
15
explain 
select b from t1 order by b desc limit 5;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	NULL	index	NULL	b	4	NULL	#	100.00	Backward index scan; Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t1`.`b` AS `b` from `test`.`t1` order by `test`.`t1`.`b` desc limit 5
select b from t1 order by b desc limit 5;
b
19
18
17
16
15
drop table t1;
#
# Try a primary key in a reverse-ordered CF.
#
create table t2 (
pk int,
a int not null,
primary key(pk) comment 'rev:cf1'
) engine=xengine;
insert into t2 select a,a from t0;
# Primary key is in a reverse-ordered CF, so full table scan
#   returns rows in descending order:
select * from t2;
pk	a
0	0
1	1
2	2
3	3
4	4
5	5
6	6
7	7
8	8
9	9
set autocommit=0;
begin;
delete from t2 where a=3 or a=7;
select * from t2;
pk	a
0	0
1	1
2	2
4	4
5	5
6	6
8	8
9	9
rollback;
set autocommit=1;
drop table t2;
drop table t0;