mysql中建表语句中key字段的疑问

Question

CREATE TABLE military_umc_organ (
id bigint(20) NOT NULL AUTO_INCREMENT,
umc_organ_code varchar(20) NOT NULL,
mt_organ_code varchar(10) NOT NULL,
create_time datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (id),
KEY organ_id (umc_organ_code) USING BTREE,
KEY organ_code (mt_organ_code) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=3823 DEFAULT CHARSET=utf8mb4;
建表语句中 KEY organ_code (mt_organ_code) USING BTREE，USING BTREE是加索引，KEY organ_code (mt_organ_code) 代表什么意思？

Answer 1

https://blog.csdn.net/kiulang/article/details/79424359