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)