# 添加索引
ALTER TABLE user ADD UNIQUE (name)

# 删除索引
ALTER TABLE user DROP INDEX (name)

MySQL添加索引Specified key was too long; max key length is 767 bytes

name varchar(255) utf8mb4
# 255 * 4 = 1020 个字节

select version()
# 5.6.45-log

# 查看数据库被限制了索引的大小
SHOW variables like 'innodb_large_prefix'

# 解除限制
SET GLOBAL INNODB_LARGE_PREFIX = ON;
 

# 查看当前的innodb_file_format引擎格式类型
SHOW variables like 'innodb_file_format'

# 修改
SET GLOBAL innodb_file_format = BARRACUDA;

create table user
(
  id int auto_increment primary key,
  name varchar(255)
) 
ROW_FORMAT=DYNAMIC default charset utf8mb4;