mysql index 8.0

创建表

use vodb;
drop table if exists test1;
create table  test1(id  int NOT NULL AUTO_INCREMENT primary key COMMENT '主键',uid int, tid int,tname varchar(12),tvalue varchar(90),createtime datetime NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',key tid(tid),unique key uid(uid)) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4;

倒序索引，Backward index scan

mysql> explain select * from test1 where tid < 10 order by tid desc;
+----+-------------+-------+------------+-------+---------------+------+---------+------+------+----------+--------------------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                      |
+----+-------------+-------+------------+-------+---------------+------+---------+------+------+----------+--------------------------------------------+
|  1 | SIMPLE      | test1 | NULL       | range | tid           | tid  | 5       | NULL |   91 |   100.00 | Using index condition; Backward index scan |
+----+-------------+-------+------------+-------+---------------+------+---------+------+------+----------+--------------------------------------------+
1 row in set, 1 warning (0.00 sec)